TigerDirect offers the Transcend SSD370 512GB Serial ATA 6Gb/s 2.5" Internal Solid State Drive, model no. TS512GSSD370, for $189.99. Enter your email address at this link to get a special $15 off coupon which cuts it to $174.99. (You'll receive a unique discount link shortly after.) With free shipping, that's the lowest total price we could find by $35. It features read speeds of up to 570MB/s and write speeds up to 470MB/s.
Note that the coupon is only valid for use once per customer.