I suspect that what you'll end up doing is only checking those spots you're most concerned about. To do a whole cage is probably possible, but very likely to be spendy. There is a crack detection process that works similar to Magnaflux, but is a dry process. Most engine shops use these for checking btwn the seats of an iron cylinder head. It won't work reliably if there is paint on the tubing though.
There are also crack detection kits that use chemicals, usually a cleaner followed by a detector, and then finished with a developer. I've not used one so I only know the generalities. I do know at least some are metal specific, i.e. intended for use on aluminum.
I think what Thom is talking about is Dye Penetrate Inspection. You clean the part spray on the dye wipe the excess wait a few minutes and spray on the developer which reacts with the dye to make cracks visible. The problem with this method is it only checks for surface flaws. This is mostly true with Magnetic Particle Inspection as well. One other thing UV or black light is almost a must.
If you just want to check the welds and the HAZ areas, then it
would be pretty quick and relatively inexpensive. It really depends on how much area you want inspected, and how well the areas are accessed. My shop does Non-Destructive Testing, x-ray, gamma, dye penetrant, mag particle, ultrasonics, basically a full service NDT shop. We have 2 mag machines at the shop, but we also have portable units.
Give me a call, we have been doing more and more off-road stuff, trailing arms, micro stubs, gears, etc.
714) 529-7291 shop
By the way, we are in Brea, and I live in torrance, I pick up parts from other racers all the time between work and home...