have my trusty Aero Precision ar15 which is tricked out with the trigger and controls I like so I was thinking a 6.5grendel upper for my lower but 6.5 ammo isn't the most popular so Im also looking at a ruger American predator in 308.

I can get each for around 450 but I only have cash for one.  

6.5 upper  keeps me in the AR with cheap plinking ammo but bought online

American I get a whole other gun plus readily available ammo at Wal-Mart

Ammo isnt my sole deciding factor but it is important.

Get a Wolf Grendel upper and use it on your lower, but start building another lower so you'll have 2 complete rifles. Ammo is getting more plentiful with 4 new additions from Federal this year, taking it up to over 40 factory loads. You have super cheap steel case available to shoot if you want, and plenty of premium hunting rounds too.

+1 for Grendel

Grendel.

So here is a question,  I've got two ARs a psa for HD and an Aero Precision set up as a reese/Precision  rifle.  What about replacing the barrel on my Aero with a 6.5 and making that rifle my Precision(group shooting) /hunting/long range rilfle

Or should I build a second upper