I don't own one, however, have been considering one.
Cost wise, there are a couple options.
Maximus from Pyramyd Air $380 in a kit with a pump. That's a good deal for Pyramyd, however, if you follow the banner to Crosman, (which isn't running as I type this, maybe it's a new years thing), there's a 25% discount so the $220 for the gun becomes $165 and I believe they run free shipping on Friday's ($18 value). the pump is $190 - 25% or about $145, so about $310 for the kit.
Filling the tank is an issue. If you don't already have an air tank and access to a paintball place to fill it, you will need a pump. The Benjamin pump works OK, and is the least expensive of the bunch. Tanks are MUCH BETTER, so if you can spring the $300 for a tank on Pyramyd Air.
So, cost wise, you are into it for $500 with a tank and if you play Crossman right, about $310 or a little more.
Essentially, the Maximus is a Discovery in synthetic. Of the two, I'd definitely go with the Maximus.
You will see a couple issues on the maximus though. The bolt pull will be heavy. I believe it's a 10 pound spring you are compressing. It's a long gun, but light. It's also reasonably accurate. shot count will be around 20 or a little more in .22. You might want to consider the .177 as it has a higher shot count with 30 or so. .177 will still kill a pigeon or rat, so might be a better choice if you have a pump. If you spring for a tank, no big deal. The Euro version (12 foot pound) gets 60 .177 shots per fill due to lower air use for lower energy at the muzzle. Still good out to 50 yards.
Sorry I can't offer anything else, this is just the research I've done so far with the chance of getting one myself. Personally, I'm, waiting for the Euro to become available in the US (haven't had the cash when it was available), It's threaded for a moderator, and from what I see, it's a fairly loud gun. So many choices in this hobby!!!!!!!!!!