HD shotty
rotgut,
if you are looking for a mossy 500, depending on where you are, you shouldn't have to shop online, Most Big 5 sporting goods carry the 500 and 590 and if you aren't somewhere that has Big 5, the 500/590 is a pretty popular choice for hd shotty and should be pretty abundant. of course, you may be somewhere that doesn't have many gun shops/sporting goods stores.
pawn shops are also a popular place for 500s/590s/870s/HD shottys
the extra cost of shipping and transfer fees while, not that much can increase the cost basis of the gun you want.
check out your local ranges, chances are they will have either a mossberg 500/590 or remington 870 for rent, try them out before buying.
IMO both the 870 and 590 are great HD guns, the 590 being my preferred for strictly HD, if you ever plan on shooting trap/skeet/hunting, the 870 is a better choice. both have a ton of aftermarket accessories.
stay away from pistol grip only. they may look cool and seem like a good idea, they are not (imo).
while practicing at the range shooting at paper is fun, if you want real practice, take your gun to the trap range. shooting at a moving target will give you the confidence and experience needed to get a decent handle of your new gun. shooting at moving targets will also reinforce proper technique and develop muscle memory that is essential proper use. using your short barrel will be more difficult than using a 30 inch barrel, and the old timers might rib you a bit for shooting a tactical on the trap line, but the way I see it, you need to practice with the gun you intend to (hopefully never have to) use. I shoot my tactical at the trap range quite often for practice.
while recoil isn't that bad with proper shouldering of the gun and game loads, slugs and buckshot can pack quite a punch. get the proper technique down before moving up to higher power rounds.
many will tell you that buckshot is the way to go for HD, which is probably true, but really, if you hit a BG with a round of game load at an "in your house" distance (read less than 10 yds) it will mess them up, bad.
good (safe) shooting
porrpk