Figure out how much you're actually willing to pay for a scope and then go from there. Lots of the scopes suggested for you here (Bushnell DMR 2, NF SHV) although great scopes, are closer to $2K than to the $650 you say you can get the Nikon for. You don't need to spend $1500-$2000 to start shooting long range.
I do suggest getting a scope with a reticle that matches the turrets, be it mil/mil or moa/moa. People will tell you that moa is if you think in inches or yards and mils are for metres/metric but that's total nonsense. They're both just angular measurements. The vast majority of PRS-type shooters use Mil/Mil scopes and all ranges are done in yards. If you're just shooting by yourself, it really doesn't matter which you pick.
FFP (although it is my preference) is also not necessary, depending on what kind of shooting you plan on doing (matches? long range plinking? F-class?) and what kind of magnification your scope goes too. If it only goes to 10x, FFP isn't a big deal cause you'll pretty much always be shooting at max magnification. Also, like others have said, good glass trumps higher mag every time. I'm not sure who makes one, but you might want to look for a fixed 10x scope with matching reticle and turrets as 10x will allow you to make hits out to 1000 yards or so. Once mirage comes into play, you won't be shooting above 15x even if your scope goes to 20, 25, infinity. A seemingly suitable scope that I believe is close to your target price is the Sightron S-Tac 3-16x42moa.