The Bottlehead is, of course, a DIY kit. It is almost impossible to beat a kit re bang for buck. If you would like to DIY it is a good choice.
The best thing about DIY is that you learn so much quickly and you can change your equipment to suit your ears without having to buy all new all the time. It's like homecooking. If you would like to DIY I suggest you go the Audioasylum tube and DIY tube forums and just check it out for a few weeks. A lot of good kits and ideas will pop up. Don't be in a rush to buy.
I'll suggest two. 1) the Bottlehead is a great product and the support there is unmatched. Doc and Paul J. are diytube saints. 2) look at the kits at www.diycable.com too. These are simple to build and great sonic bargains. Kevin and Brian are also good guys. You can get in under your budget there with the Ella(EL34) or Joplin(2A3) kits. These sell for about $600. Neither needs a pre. You can do some improvements/modifications later on.
After you've looked make sure you listen. And make sure you have a good match with your speakers.
If you want to learn a little about tubes here is a great on line source:
As the URL suggests this is book 6 on tubes. If you hit the home button it will bring you back to the general index and the entire section under "Electrical Engineering Training Series" is well done and understandable. It's a government publication!!! They do something right.
Cheers and have fun,