While I do like the AR if I was choosing between the two I'd go with the M1 simply for the fact as stated they are not going to get any cheaper. I have a lot of love for old battle rifles and the M1 is a great piece of history that you can take out and have a lot of fun with. the 30 06 round packs a hell of a wallop and can be accurate for days! I don't see the AR going anywhere and the prices have calmed down on those enough now where you can look around for what you really want your AR to be like and not have to worry too much that the price or availability is going to change any time soon.
I've got AR's, AK's,SKS's, 30 carbines, Lever rifles and 22 plinkers. But my long gun collection will never be near complete until I put an M1 in it.