Here's one I found today. 600GB Intel SSD for $250. It's the older 320 model SATA2 only. These are well regarded as reliable which is why I think they could be good drives for older Dell C6100's or even Xeon E5 v1's that had so many SATA2 ports.
I tried $200 and didn't get it but here's the link. They have 10+
Intel 320 Series 600GB 2 5" Solid State Drive 2 5" SSDSA2BW600G3 SSD 0735858219808 | eBay
I tried $200 and didn't get it but here's the link. They have 10+
Intel 320 Series 600GB 2 5" Solid State Drive 2 5" SSDSA2BW600G3 SSD 0735858219808 | eBay