I'll be the dissenting opinion here:
Unless you can only afford one gun, ever, in your entire life and you'll need to do everything other than CCW with that gun, I don't see any need to get a shotgun first.
They are versatile but a lot of what is called versatility is just people trying to force the gun to do something it's not well suited to.
They're great for close range SD with a short barrel. I owned one in this configuration and it was very well suited for this - I never felt unsafe with that Mossberg loaded with buck shot near by. But these short barrels will often be IC or unchoked, which means patterns with regular shot will probably be too open for anything other than close range defense. They may also shoot slugs pretty well - mine did out to about 70 yards. But it still wasn't a rifle.
Long hunting barrels are great for hunting but they're often too long to be easily handled for defensive uses.
Rifled slug barrels with sabot slugs are reportedly often effective out to about 200 yards but I'd bet that the trajectory/ballistics are nowhere close to ideal.
Sabot slugs are also expensive, probably $14-$17 per
FIVE round box.
OTOH, Mosin ammo is about $60 for
440 rounds. And 30-30 Winchester SP hunting ammo is about $12 per
20 rounds from Federal, Remington, and Winchester. Just food for thought.
It may be possible to split the difference - maybe a 22" barrel with interchangeable chokes and rifle sights would do well.
If I were going with a shotgun that I wanted to do everything with I'd try to find something like this. But I don't think I've ever seen a shotgun in this configuration used in any store. The ones you normally find used for $150 are plain field length guns. If you start with that, by the time you factor in all the specialized ammo and the extra barrels you're likely to need, it might just make more sense to buy the nice used 28" Mossberg 500 for small game AND a Lever action 30-30 or some other inexpensive rifle for rifle stuff.
No disrespect meant for the shotgun or its supporters.
Some of them will make arguments against what I said and they'll probably have some valid points.
And, I still have a couple shotguns and will probably have at least one more before I'm finished buying guns. I also still keep some slugs around for my 20 gauge because they do add some capability.
But I understand that it's a shotgun, not a rifle.
As for me, if push came to shove, I'd want a minimum of a three gun collection:
- A good centerfire rifle. We've already covered the budget choices for these.
- a good .22 rifle.
- a reliable, somewhat concealable centerfire handgun