Hi, if you have mechanical skills, tools and some welding experience then it's dirt cheap as steel tubing is quite cheap but very strong.
I paid A$150 for enough steel tubing to make 2 CNC routers as shown in the photo.....that means the complete frame of one router cost A$75.....it was cheaper to buy a full length of tubing and cut it to my sizes at home.........I was going to sell the second one once it was finished.
Attached is a model of the finished CNC router in Polystyrene material to make sure the proportions of the build were right and get a feel for the construction before committing to steel.
Ian.