IMO I call a beater a road bike you find in a yard sale, or the dumpster for under $15 bucks. Redish the wheel, take off derailleurs, and clean it up. Viola- I call that a 'beater,' since I really wouldn't care about it, AT ALL. I use that for quick errand runs, or in bad areas of town, etc.
I don't have too much money to play with stuff. My 'nice bike' is my Fuji Track 06, mostly stock-$500. After that I dropped $300 on a new wheelset, IRO Deluxe. About $100 on misc. parts- new stem, seat... masterlink type chain.