For $200? It depends. How much MORE money do you want to put into the machine? If you want the system to run a newer OS than Lion, you will need to buy a new video card (50-200 dollars, depending on selection.) You will FOR SURE need more than 2GB of RAM. Often, there are Ebay deals on non-Apple RAM for reasonable-ish prices. 16GB of FB-DIMM 667Mhz RAM can be found for ~$60 in 8x2GB configurations. That is the MOST economical config, as far as I know, since 4GB FB-DIMMs cost a fortune. The machine will also take X53xx Xeons, which can bump you to 8 cores if you need the power. 2 X5355s (2x quad core 2.66Ghz) will run you another ~$50. Then there's the hard drive situation. If the tower comes with a stock hard drive, you'll most likely want a new one. Depending on the size you need, or if you want to get a PCIe SSD, it will cost somewhere in the $50 (1TB Spinner) to $200 (Velocity Solo x2 and 128GB SSD) area. And EVEN THEN, it's a bit of finagling and work to get newer OS's installed. Mavericks has been very easy, thanks to Tiamo, and though I personally have not tried the Yosemite beta on my 1,1 it doesn't sound too tough.
Sorry for the word vomit, just figured you should know what you're getting into. Those numbers are a bit arbitrary, I haven't shopped for parts in a while, and you might be able to get or forgo some of those upgrades for cheaper now. I hope the info helps though. The 1,1s are still VERY capable machines, if you put a bit extra into them.
-N