Unless you're already a darn good shooter, I'd plan for ~2 MOA targets (16" at 800 yds, 12" at 600 yds, etc). Clean misses are frustrating, but more importantly, correctly estimating misses can be tough in the dirt, unless you have a near vertical backstop very close to the target. Knowing where and why you missed is about the only way to get better.
If you're willing to put in some work, and deal with bulky target frames, you can save a bit on homemade target stands. I use the cheap "DIY" saw horse brackets and 2x4s. For the hanger straps, I cut out the sidewalls of old tires (free at a tire shop most likely). You can get 4 targets worth (8 straps) from 1 tire. With bolts/nuts, brackets, and wood, the stands are only about $20. I screwed some eyelets into the feet, and use the cheap, "nail" style, tent stakes to keep the stands from falling over with big guns.
The stands will take dozens of hits before needing replaced. They do tend to get filled with shrapnel and splinters though, so wear gloves when handling them after they've been used a bit...
Ebay is a great place to look for targets. I found a couple vendors that had free shipping, and got plates far cheaper than any "major retailer". 3/8" AR500 is plenty for all but the craziest rifles (past 100 yds anyway).
This guy offers 20% if you buy 2+ targets, and it appears you can mix and match sizes. I think it's one of the vendors I bought from with no complaints.
With discount, the prices are as follows...
16" ~$72
12" ~$28
10" ~$20