I don't know about pricing, but it probably would be at least $200 from Mesa. I have not seen any head cabinets recently on Ebay, but you might check there.
As far as ease of transfer, if you get the head with a fan and Reverb Tank already installed, then it is incredibly easy. I used to do this with mine.
The drawback for me was the fact that Mesa heads of this style have a hole in the bottom and the Reverb Tank actually sticks out a bit.
I used to have my Rectoverb sitting on top of my 2x12 THD cab, and my Mark IV head sitting on top of that so that my kids couldn't get to the knobs. It used to drive me nuts becuase I had to put books under the feet on the head so that the handle of the Rectoverb wouldn't hit the Reverb Tank. The amp would totter back and forth if I didn't do this.
Other than that, I didn't notice any real disadvantage to the head. I'm gradually becoming more of a combo guy and don't really care for heads that much. I need the convenience more than I need the lack of weight.
The Mark IV is a popular amp, you should get some more responses. Hope this helps.