you can get the bottom metal from Badger ord
. It runs about $400 +fitting by your smith.
This only works for a 308 or 308 based cartridge, 243, 260, 7mm-08, 308, 358 win. So you can't buy this system and convert it over to a 22-250 or 223.
I am going to say this will end up costing you more then the entire SPS rifle did and for what nothing really.
You can go with a CDI version
for a little less money $302 or the H-S version
for even a little less $278 - $300
Do you really need to reload that fact? I myself just stuff the internal mag full and one in the chamber then I load my pockets up with about 10 more (when Ground hoggin)....