You can get SSDs for $60 & $70 if you look. As others have answered, they are backwards compatible, so any drive you get should work on your SATA II machine. People have recommended the Samsung 840 EVO, which is a fine SSD, but don't forget to apply the
patch that was just released. That drive could lose performance over time, otherwise.
The Samsung 840 Pro is a better option, but it is closer to $100 for the 128GB model.
There is currently an Intel 256GB at Newegg for $109 ($99 with code). This is a nice brand, but apparently a slower drive. Which I guess means instead of "really super fast", it's just "super fast".
I looked at your system and I have a suggestion. My guess is you're working with 2 or 4 GB (I don't see it on your spec sheet), but I do see you can max it out at 16GB. I would suggest getting a budget SSD, like a Sandisk, OCD, or something... and also upgrade your memory.
I would suggest at least 8GB, which would mean 2x 4GB DDR3, and your board only reads up to 1333 MHz, so get 1333 MHz or higher, if the price is right.
Is 8 GB necessary? No.... but it can only help.
If you are using the onboard graphics, then I would definitely look into a graphics card for that PCIe 2.0 slot that's available.
Anyway, hope you find what you need.