I have to disagree with most everyone here. I think the .500 S&W is a fantastic plinking gun. Well, not if you limit plinking to going out with your kids and shooting at balloons and animal crackers. If your definition of plinking is shooting for fun and entertainment and to practice then the .500 is great.
Start with "I wonder if I can shoot through (insert any large object that is handy)?" and go anywhere you want to from there. Large pieces of firewood that haven't made it to the splitter can be fun. Old lawn mower engines (be careful of flying debris and clean up after yourself) would be a hoot. Digging up gopher holes and shooting them when they come out to close the hole could be fun but you might get your gun dirty. Shooting at large dirt clods or the odd group of weeds 500+ yards away in a plowed field is fun with a .22, more fun with a .44mag, and even more fun with a .500 - the only problem is that the cloud of dust can make it hard to tell the near misses from the hits.
As far as ammo goes, I would avoid the Ultramax 330gr. lead bullet loads because they will lead up your bore in a hurry. Ultramax has some 325gr. JHP loads at 1400 that are about $3 more per box. The difference in cleaning time will probably make up for the difference in price. Magtech has some loads that are $4-$5 more a box that could work for you as well. Any of those loads will also work nicely for deer-size game.
That being said, reloading is the only way to go as far as feeding the beast. It still won't be cheap, but it will be cheaper.