LOL I am 'saving' money by using titanium rather than high-grade stainless. I looked into making my own bushcraft knife and while a reasonably tough steel like 440C was a bit cheaper than Ti, anything better was double or triple the cost. IE a strip of 440C 3.5mm x 75 x 900 was $115, so building an entire frame would be pricey and still not as tough as Hardox or an equivalent wear steel.

There is a Sandvik stainless called 12C27 that might be cheaper in Europe and the UK; its similar to 440C so its fairly tough and can be hardened. I hear that it is manufactured in sheets, so you might be able to get it cut-to-size or have parts water-jetted.

My pick for the 'best' stainless steel for a bot is Damasteel. It is made like damacus steel and looks like this:



Its so pretty that nobody would want to hit your bot and spoil the pattern