I started a build on a quarts oven I rescued from a landfill. It has a nice small form factor and a glass door so I can see what's happening inside.
It does have quarts tubes, but they were of low quality, and their power was a bit low.
So I bought a bunch of tubes from Aliexpress. These are not the cheapest, (Around EUR10 each) but they have a much better quality. They have cemented on ceramic end caps and you can buy them in different lengths. And you can buy a few spares of the same size.
The metal of the oven was very thin, so it was not very difficult to take the whole thing completely apart, punch some extra holes in the sides and replace the 2 old tubes with 6 new ones. Because the end of the ceramic end caps is thinner, if the hole is the right size, you can put both sides of the oven over an end and don't need any other mounting materials.