I am going to slightly disagree with the previous posters. It is a worthwhile purchase to slowly upgrade.
If you are going from nothing, a $100 receiver is a fair upgrade. I went to a $50 Insignia - 5.1 receiver, using Athena speakers. And it is great for me. 550W, but no HDMI. Has 1 digital (That I don't use) and 1 optical (Which I use for my PS3). Now, I don't get lossless audio, I don't get HDMI support, and I don't get 7.1 channels. But, it lets me have something, while I save up money for something else.
Here is the question that I asked myself - would I rather wait 3 months and have nothing? or wait 9 months, have a decent receiver right away, and then upgrade to a better system?
I chose to get something cheap now, and upgrade slowly.
Matthew