Apple uses custom form-factor SSDs in Macs, so you can't just buy any drive from NewEgg. Currently, OWC is the only source for aftermarket SSDs for MBPs, but the downside is that they are slower than the SSDs Apple use (OWC's are just two SATA 6Gbps SSDs behind a RAID controller, which means awful latency and random performance). Your best option is to seek for replacement Apple drives on eBay, although those won't be cheap.