I think JD nailed it above and I can't really offer any low cost suggestions for a scope that meets your needs Chris. Only thing I can think of is watch for bargains and even used models. Right now I remove my BUIS then mount a scope on a 1x5" riser which allows it to clear the upper and the FSB.
As far as FF rails, I need to wrap my mind around their benefits more. I don't intend to mount anything except a light on the front of my ARs so have stuck with standard handguards on one and MOEs on the other. JD has made excellent points here and elsewhere on quality rails so this is a decision I have to come to terms with this year. Oh don't you love BRD!