[dan35]

That price's really a bargain for that server. If you're looking for a single core Intel P4 or AMD Athlon 64, you should raise ur budget at least to $100 (or a dual core to $150).

Semprons outperform Celerons, but a 2.8 GHz P4 will out perform a Sempron (say 2800+). Think of an old Sempron as an Athlon XP, as they are basically the same chip. New socket 754 semprons are athlon64 base with some cache turned off.
Semprons make pretty good entry level servers, better than Celerons. However, if you need good performance go for a P4 2.8 or an Athlon 64.