The world isn't divided into "poor" and "rich". A chair for a programmer, particularly an independent one, is one of the tools that you need to work effectively.
A friend of mine is an independent auto mechanic who has been in the business since he was 15 (about 20 years). He now owns a small shop, and probably nets a good "salary" similar to many IT professionals ($90-150k). Not rich, not poor.
Guess what? He doesn't use a Craftsman mechanics toolkit from Sears. He has an long-term investment in high quality tools from vendors like Snap-On to the tune of $50-60k. Cheap tools would cost 1/3-1/2 that, but guess what -- a broken wrench means that he isn't working, and his time is worth $90/hour, and the high-end vendor comes to him, so he doesn't waste time in stores.
As a programmer or IT type person, your brain is your primary tool, but it depends upon the working order of all of the supporting tools in your body to perform optimally. When your job involves sitting on your ass for most of the day, a proper chair is just like a $75 high quality wrench for a mechanic -- a good investment.