My laptop has a TOSHIBA MK2555GSX SATA 250GB 5400 HD on it. I'm thinking of putting a SSD in its place but I'm not sure which one to buy, if I google the name of my laptop and SSD I get expensive options and I'm not sure the regular cheaper options found on slickdeals are compatible or not

Can I just put any SATA SSD on it?

Pretty likely the interface in your laptop is only Sata2.0 (3gbps). Most new SSD are Sata3 (6gbps) but are backwards compatible, so no worries there.

Most SSDs are 2.5" (which you need), but there are some that are 3.5" (normal desktop drive size) and some which are mini-pcie connectors. Make sure you get 2.5"

You should check in the BIOS and see if your sata can be set to AHCI mode, which generally improves performance of SSD and should really be done before you reinstall windows to avoid the headache.

summary: Most 2.5" SSD should be perfectly compatible with your system. Get at least at 120GB IMO. Do it! Do it now!

You are right, its SATA 2