You can make your own foam for the seats. I can help you with that.
You'll need a couple of special tools. They're not real expensive. Most you might already have.
Need a compressor though. But even that could be worked around, if you don't.
A cheap-ass pot style spray gun. $20.00? Some glue. 'Automotive Trim Adhesive'. Smallest size is one gallon.
An electric carving knife. The one for cutting up a turkey. $20.00 for a new one? I get 'em at the Sally Ann. $5-6.00. I burn out a couple a year. Check to make sure both blades are moving. That's a broken part inside. Not worth fixin'.
A woodwork style bandsaw is the perfect tool for cutting foam. Especially larger pieces. But not everyone has one of those just hangin' around!
Some felt pens. A long straight edge. A drywall ruler with the end piece knocked off. Or a Carpenter's 'T'.
Some Burlap.
A bunch of 'Hog-Rings' & the H/R pliers.
A good pair of scissors. If they'll be used just for this, there'e some pretty good ones out there for cheap. I spend just under $100.00 for mine, but they'll last 5 years of almost daily use/abuse.
Look up 'Upholstery Supplies' near you. Some of the bigger specific wharehouse guys require tax numbers or a Biz reggie to get in. Some are store front retailers. Around here, there are places called something like 'The FoamShop'. If they don't have most of what you need, they'll be able to get it. (From the big wharehouse guys! Of course!) They should have things like the glue on the shelf. Figure on a 30-40% mark-up in the store fronts. If you find an auto upholstery shop near you, they might be persuaded in selling you some of this stuff. Either way, if that doesn't help, I could get you some of it. I just can't ship any glue. Besides the foam, you could have all the stuff you need to do this for $100.00 or so.
If your willing to go that far, I'll get on to the foam part.
Here's a couple of pix. 1st just shows the different densities & how the foam was shaped.
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This is the pic in my avy. Seat out of a '56 Ford F100. It's the original one that used to look like it was out of a school bus. The foam work was done with an electric turkey knife.
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