What kind of amp are you using. I know some brands like Fender and Mesa use common chassis for both head and Combo versions of the same amp. I see people selling empty used head cabinets on ebay all the time. IMO putting your amp in one of those would be the easiest/cheapest way to go, if you can find a cabinet that fits your amp.
I believe the chassis is mostly the same for some amps, so it shouldn't be a problem as long as you find something that holds the chassis firmly in place. :32:
Get one of those collapsible trollies - you know the one that you can pick up from the DIY store - and put your combo on that - you can then wheel it around. That's what I have and use for my amps. I think that they are reasonably cheap and are probably going to be less expensive than converting it to a head.