You need to very carefully decide what you plan to do with this truck.
If offroading is your focus, there is no better tranny than an SM465 (or 420). That swap is well worked out and is great low gear bang for buck. It's not so great on the street, but it isn't terrible either.
If street driving is what you are after, the first gear syncro of an H42 or H41 is more suitable.
If it were me, I would start at the logical place-the tires. Be serious about your needs. You live on the East Coast. Explain why you "need" 37 inch tires. I don't remember Florida as having much in the way of offroading, and the highest hill is 300 feet. 35 inch tires will simplify your gearing needs and 33s even more so. 37 inch tires and 3.70 gearing is just going to suck, no matter what transmission is in front of it.
If you are determined to run 37's, then the next logical place to look is your diffs. 4.88s will be a good match for 37s. It won't give you crawling gears, but it will make the current driving you do much more enjoyable with less stress on the clutch and other driveline components.
Continuing to work backwards after the tire diameter and gearing are a good match, you have basically 2 choices. Low gearing in the transfer case is all good. You get to preserve the good street manners of your current tranny and you get great crawling gears and a much stronger transfer case (Orion). It isn't a cheap option, but it's a very good one. The second choice is a stock transfer and a low geared transmission, like the SM420 or 465 you mentioned.
No matter what, assuming you want to stay with 37s, re-gearing the diffs is the first move to make. After that, check your bank account for further options. In my view the best of all worlds would be an 4.88s/H41/Orion. That covers all your bases, keeps mostly Toyota parts.
A $1500 budget isn't going to get you much, so you need some honesty with your self and your intended uses. Do the 4.88s first. If they are as cheap as you say, you may have enough left to do the next cheapest thing, which would be an SM420/465. That would be a decent offroad set-up.
In this discussion I didn't see anything mentioned about lockers? If you are serious enough about offroading to need 37s, you also need lockers. If not, buy some 31-33 inch tires and all of your gearing problems begin to disappear.
Just remember that none of your options are cheap, and if you cut corners you will end up with less than you started with, not more. If you really want to do things correctly, you need triple your $1500 budget. I'm not kidding.
Just to regear diffs:
(approx)
4.88s $400
Bearing kits $250
Professional set-up $300 (this assumes you pull the 3rds)
