stanislaw, I think the jetBook Lite meets your requirements.
Not only does it read txt, it comes with 100 txt files (books) on it!
It has pdf reflow, which I have been quite happy with.
And it reads rtf very well. rtf is the favorite format of GhostHawk, a jetBook Lite maven here.
Newegg.com currently has the jetBook Lite on sale for only $79.99. Newegg's prices change from week to week, but the JBL is usually the least expensive reader available.
http://www.newegg.com/Product/Produc...Lite&x=16&y=26