Buying a bike on ebay would violate my $100 rule. I don't buy anything over $100 that isn't in my presence as I pay for it (well ok, I fudged a few dollars for a couple of items this year).
If you are not in a hurry, and willing to shop, there are some great ebay buys to be found. Some of my purchases the last two months:
used Shimano 600 road brakes - $11.62
new Truvativ Touro triple crank - $30
new Vuelta Starlight wheelset with 2 Michelin Pro Race 2 tires - $115
new Sram PG970 11-34 9 speed cassette - $33.46
new Sram trigger shifters - $29.04
Those prices all include the shipping. The deals are there, and it sure made building a bike from a frame (and upgrading it) cheaper than I thought.