You could try something like the K-12G kit. $190 http://store.tubedepot.com/diy-k12m.html

Infinity Primus P162s are overachievers that should get a listen. They are efficient enough for use with an 8 wpc tube amp. Don't be fooled by their $200/pair price.
http://www.stereophile.com/standloudspeakers/1007inf/

I'm not sure why you would want an inexpensive tube amp unless you are after "tube sound". In my experience inexpensive tubes sound like inexpensive hifi. High quality transformers don't come cheap and the transformer(s) become the heart of any tube amplifier. IMO you're better off avoiding tubes until you can spend the money for a very good tube amp.

Consider a simple system comprised of powered speakers; http://stereophile.com/standloudspeakers/1207ae/

Home-built does not mean home designed. It is the execution of a good design that you are after. You want good design and excellent parts. After that many a Dynaco ST 70 has survived the decades to make the owner happy with their efforts. Unfortunately, the days of the ST 70 kit are long gone.

Tubes still revolve around parts, more so than transistors. I think you'll find most competent designers telling you it takes great skill to produce a workable design with minimal parts - Nelson Pass has been at it for almost four decades and still is refining his work. More parts means more money to maintain excellence of parts.

I'm going to guess that your budget has kept you from exploring the options available at an independent audio shop. So you are looking for options that you probably haven't heard and cannot audition before making a decision. That's not the best approach to getting "clarity and flat/accurate response" any more than obtaining those qualities ensures an enjoyable system. However, consider that your goal of "flat response" alone is virtually impossible with most inexpensive tube based amplifiers. Once again it takes great skill and goodly sums of money to produce a transformer that drops the output impedance of the amplifier to a level where it does not interact with the meanderings of the speaker's impedance load. Ohm's Law then says flat response goes out the window.

I use tubes and have for decades, I wouldn't swap for a transistor for my needs and wants. But I would caution against making your first system based around tubes and certainly not based around inexpensive tubes. If you want to try the system Jackfish has suggested, it's your money. I have no direct experience with that specific amplifier. I just have enough experience with inexpensive tube amps to provide a word of caution about their generic kind.

My advice would be to save up for tubes and buy something worth owning. Kits are fine if you have good soldering skills. Those skills are more difficult to acquire than someone without good soldering skills assumes. Without good soldering and construction skills, you will have a constant problem on your hands and few people who can help get you out of a mess. The amp listed is mounted on a board. This is a danger to you and anyone in your home as tubes have lethal voltages in their circuits. Exposing those voltages for anyone or any animal to touch is unwise. If you do not have the metal or woodworking skills needed to complete a project such as this, I would consider other options.

Why not try a shop and ask about trade ins that might work with your budget?

get a pair of audio engine A5s and be done with it.

http://www.bhphotovideo.com/c/product/533715-REG/Audioengine_A5B_A5_Bookshelf_Speakers_Black_.html

they get really great reviews.

ummm....."clarity and flat response" are not characteristics one associates with tube amps as a whole.....really well designed ones have those trademarks, but most of the ones ive heard color the sound in some way(which is precisely the attraction to me). Why tubes?

Quote:
Although sound quality is important to me, I don't soon see myself joining the ranks of audiophiles anytime soon. I don't want something that sounds bad. I enjoy clarity and flat/accurate response.

Does anyone have experience with home-built / low-end tube amps? I don't want to drop a few hundred dollars into something that will be painful to listen to.

The sub-$500 market for integrated amps provides plenty of choices. You can choose from Rotel, NAD, Onkyo, Cambridge, Arcam, etc.

If you're not going to buy speakers with this budget (that's what you're saying now, right, no speakers?) I think there's a Vincent integrated around your price range.

Just check the equipment reports in the Stereophile archives for some ideas on how each component fares with various types of music. Or you could try numerous small companies sold through the web. Most internet only retailers offer 30 day trials.

Either you hear differences between components or you do not. If you don't, then buy what suits you in other ways. If you do, then you really need to identify what it is you want from the system as a whole, not just from the amplifier, and try a few pieces to find what you like.
"Sparkly warm" isn't quite the explanation you'll need. As a rule putting a BandAid on a problem by using the opposite approach (warm/bright or forward/laid back) generally fails to impress over time and wide ranges of musical styles.

You don't need a lot of watts, quality watts are better than more watts in virtually every instance. The same goes for other specs, listen rather than look.

I really think you would do best in a dealer's demonstration room listening to amplifier A or B and making decisions based on what you hear and not what you have trouble describing. Are you near any audio retailers?

http://www.stereophile.com/reference/50/index.html