7mm Rem Mag factory ammo won't be cheap in any quantity. It runs around $35 and up per 20, depending on the bullet. You might get a bit lower price by ordering 5 boxes. Money up front.
The .223 depends on where you are and what kind of ammo you want. Factory 55 grain Remington runs around $22 per 20. You might find some 'White Box' for a bit less.
.22's should be readily available by the 500 round brick or you can order a case of 5,000 in your local gun shop. Money up front for a case though.
In any case, if you haven't done so already, you should be finding which brand your rifles shoot best before you buy in bulk. Try a box of as many brands, of each cartridge, as you can first. And keep the brass. You'll be reloading sooner or later.