Did you mean 2x512 or 1x1024? You should get two sticks for a S939 (dual channel).
For some cheap TCCD (good overclocking RAM chips), try and save up a little bit more; I don't know of any for those prices off-hand (other than Corsair/Mushkin value RAM for $140, which you don't want if you plan to run 1:1 at any overclock past 220). You may be able to obtain some good stuff for $200-$225, though (Patriot/PDP, G.skill; I've actually seen a pair of Patriot sticks at PC3200 2-3-2-5 for $183 at Newegg, though these particular ones aren't the TCCD you're looking for... my idiot brain found that out a few minutes ago).
If you had meant a single DIMM, you can probably afford a value DIMM at PC3200 CL3. Big modules like that are a little harder to overclock, from what I've heard.