It has a lot to do with what you're comfortable with.
I've rebuilt a few myself, had some rebuilt by people I trust, and bought factory rebuilds. Of the ones I rebuilt or had someone rebuild, most were the OEM carburetor that was on the vehicle (mostly two barrel Carter BBDs) and a bought a few rebuildable cores. (Rebuildable core is what the $45 one is.)
Part of what you're paying for from Rockauto is a warranty. So, take a careful look at the warranty before buying, if you go that route.
For price comparison, see what Edelbrock wants for a new carburetor.
Edelbrock bought the Carter AFB molds and tooling machines when Carter went out of business. So, Edelbrock carburetors are essentially Carter AFBs and many of the parts interchange. (It's my impression AFBs were more widely used than Thermoquads.)
Another possibility, as long as you can afford the extra cost, is an aftermarket electronic throttle body injection (TBI) conversion.
A third consideration is you mentioned maybe converting to LPG (propane). As long as you're messing with the fuel system, it might be worth converting now instead of rebuilding/replacing the gasoline carburetor.
