It is not very difficult to convert an old TV trolley into a welders trolley, just a couple of supports and cut a hole for the gas bottle and you are done. The trolleys are getting a little harder to come by but check the local op shop or local tips recycling center and tell them what you are after as many would go straight to the rubbish but they may grab one for you.
Depending on the trolley you may need to weld a little extra strength to support the weight on the top shelf, in my case there was was two uprights needed at the 'front'. A little bit of pipe to hold the gun is handy too.
Having recently upgrade to Gas welding it was a case of repositioning things so that hoses and leads stayed within the confines of the trolley and hacking a hole for the cylinder to slip through the top shelf.
On the bottom shelf I carry my mask, gloves and few other items like magnets, wire snips and clamps.