Yep, I too have a tendancy to gather random items to make terrain.
This stems from my own early gaming days in Jr. High and High School, not that I was so terribly cheap (well, yes, in truth I was), but also there just wasn't very much available way back then (when the earth was waste and void), and I didn't know many other miniatures wargamers to learn from. So I had to make due with what I could find and what I could create from my own imagination.

The Russian peasant hut is balsa. I bought a single long rectangular strip, and a single semi-circular rounded strip, and managed to make about 15 peasant huts. Took some time with a razor to score up the thatched roofs.

Here you can see many of my "made-on-the-cheap" terrain items.
First, my terrain itself is done with a felt table cover and painted elevations. The elevations I have created by cutting up corregated cardboard. Any box that comes in to my home is likely to get carved and painted. Typically green on one side and sand/tan on the other. I often just place my tanks on the cardboard when I spray paint their base-coats, so that I don't even really pay for painting my elevations.
Note the churchyard. The church itself is a commercial model, but the yard has a hedge made from the kitchen scrubbing pad that was mentioned by AuCav above. The grass of the yard is model railroad paper grass -- not too enthusiastic abut that stuff, haven't used it much since. The gravestones I cut from regular cardboard.
You'll notice I also use pipe-cleaners for hedges. I've also sprayed some pipe cleaners stone gray to use as stone walls. Not the best modelling you'll see here, but functional for a quick set-up game.
I also bought a triangular-cut balsa strip. With rectangular and triangular strips you can make almost any shape. So you see many buildings made from the balsa. Total cost for the materials to make about 30 buildings (between peasant huts and whatever else) was about $2.00. I still have plenty of balsa left over. I also taught myself to make molds and do resin castings, so that I could more quickly duplicate those buildings that seemed to come out well.
Behind the church, barely visible, is a water tower. Made from a base of the balsa, with a cut section of cardboard tube from a pants hanger as the tank itself. There is also some lichen in the back along the creek. I started with two boxes (small boxes) of colored lichen as my primary means of modelling trees. Bought them when I was about 15 at the model railroad shop. Still have some of that stuff in the kit, although after 30 years its getting a bit dried out. So I gather fresh lichen from the trees around my father-in-law's house when I visit over the holidays. Yep. Still do. He thinks I'm a loon.

Felt cloth table. Corrugated cardboard elevations. Tape roads and rivers. Felt cloth cut-outs with model railroad shrubs and flock for cultivated fields. Cut chenile (like giant pipe-cleaners) mounted on pennies for pine trees. Nails with model railroad shrubs glued to them, mounted on pennies for disciduous trees. Buildings mostly home-made from balsa strips. Bridges scratch made from cut carboard (notice the girder bridge in the distance ... one of my favorites).
I don't spend much on my terrain ... use my money to buy more tanks.

Here I'm mixing my scratch-built stuff on some of Thunder's nice gaming boards. I've added sand to make dirt roads, and put my blue tape onto some of his roads to convert them to streams. Some of my buildings are added, most notably the factory complex in the distance. That is another of my el-cheapo approaches. I take plastic packaging and cut/paint it to make buildings. In this case it was the plastic keyboard cover that came with a new computer.

Another view of the factory complex. Also a wooden girder bridge in the background, again scratch-built from cut carboard.

And finally a couple looks at what can be done just by cutting and painting plastic packaging. These buildings housed some parts I bought at the auto parts store, I think. Can't possibly remember what was in them. Don't even own the car anymore. But I still have the plastic from the packaging!
(Oh, and the aircraft are also scratch-built. The Gazelles are newest ones here, and I made them more than 20 years ago!

)
Hope that helps.