Are all the FD engines the same, just with turbos bolted to some of them? If they are different what are the engines called, and how much more does a twin turbo engine cost than a non-turbo engine?(just the engine)

l am pretty sure that they both have rotary engines

There was no RX-7 FD non-turbo.

yes there is an FD3S non-turbo (type-x).did not get manufactured here in the U.S.
twin sequential turbo-13BREWTT
non turbo-13BREW.

All FDs came from the factory as twin turbo. There are no NA ones, unless performed by the owner. Even the Type X is identical under the hood as all other FDs. They're all 13B-REWs, which stands for 13B-Rotary Engine double turbo (W is easier to pronounce than twin for native japanese speakers).