I'm going to be running an in person campaign for some friends sometime next year (hopefully obviously). Ive been trying to find a place to purchase some basic items for terrain and things of the sorts. Fortunatetly i think im covered on Mini's for different monsters, but im hoping to find good places online for shopping for other things for map building and what not. I do know of 2 local shops that i want to do some shopping from to support local, but as we all know they CAN be a bit pricy at times, which is obviously justified. Just hoping to find suggestions for things to look for is all.

Dwarven forge is pretty much the gold standard, but it can be very pricey. 

Dwarven Forge is definitely the "Gold Standard", and you'll be paying for it.

I picked up both the Core and Starter Dungeon sets (unpainted) for about $130 /w shipping. That's enough to almost fill an 18in x 24in play space and accommodates a satisfying number of dungeon room designs. (I used a cheap picture frame, removed the acrylic, added 4 pieces of sheet metal to make it magnetic, and printed 6 pages of grass texture for a texture layer. Dwarven Forge sells magnetic terrain trays, but they're smaller and add to the cost.) 

However, that's only "dungeons" and only one level. Stacking pieces to make elevation consumes a lot of resources and cutting foam takes time. In order to build any other kind of terrain, I'll probably need to spend at least that much again. This is excluding details like tables, barrels, and other accessories. (I make extra doors and curtains by slipping cardstock between the magnetic tiles.)

Enthusiasts spend tens of thousands on sets.

That said, Dwarven Forge is very easy to use.

An alternative is WarLock tiles.

You'll pay about as much for a starter set, but they are two-sided (stone/wood), and separate floors and walls, so you end up with more useable real estate.

But, WarLock tiles use sharp connecter pieces and is time consuming to assemble. I watched a comparison video, and the host said it took him about 40 minutes to build a space with WarLock tiles, whereas he only spent about 5 minutes arranging the Dwarven Forge tiles. He also complained that his fingers hurt after working with the WarLock tiles.

There are a few game stores/venues that offer in-house rentals, where you can host your games in their private rooms with their library of tiles. If you are lucky enough to have one near you, that may be your best bet until you're ready to throw down some cash.

Unless you've got plenty of liquid income, (or even if you do), I'd recommend buying a cheap monitor/TV and using it to play on a portable Virtual TableTop. 2D play isn't as exciting as high resolution 3D models, but the infinite adaptability of digital maps/resources shouldn't be understated.

3D models may be best suited for a Critical Role-style Combat Highlights, rather than large scale "terrains".

If you want to put the time into making your own.. HirstArts is not a bad place to start. Even if you don’t use his products, the tips section of his website has a lot of good info for anyone with an inclination to craft their own terrain.

Local craft stores may have stuff for miniature train setups, or at this time of year little Christmas/winter village scenes. I've gotten a lot of nice trees and small town things for quite a bit less than stuff that is exclusively made for gaming. Also, sounds dumb and obvious but you can make some pretty decent outdoor scenes with just rocks, moss and sticks you find outside. Just need a little hot glue and you can make all kinds of stuff with little cost.

You can make your own cheaply, if you want to put some time in. On YouTube the DM’s craft has a bunch of videos on making terrain cheap like Large Rocks or Trees and more. Black magic craft and others have some good tutorials as well. 

Less pricey would be books with 2d pop out pieces that you can mix and match to create your own maps. Of course they are less cinematic but only a friction of the price of 3d.

You could also look for 2nd hand and hope to get lucky. 

Now for buildings or trees, get up early tomorrow and go to your nearby dollar store, they hopefully have a lot of the Xmas village left, I spray painted them white then repainted.  Now if you need a lot of pieces, either buy or hire someone with a 3D printer.

Depending on the kind of terrain you want, you can do a lot yourself.

This is DND, not 40k so terrain is pretty secondary.