The basic FG alloy diff housing (FG #8484) is less than $100 and you can reuse you bevel gears. You can get it from FG Performance RC or RC Nuts. The attached picture shows the housing. I think it also includes an outer sleeve.

I put an FG 8485 limited slip unit in my car. I needed new bevel gears so I had to go with the full assembly and had to have new FG outdrives too. If you reuse your FH bevel gears you can use your FH outdrive cups.