[cbush]

Unless you just feel the need to update your main panel- and depending on its age, their might be value in that, the affordable solution is to go with the sub panel. I have two sub panels in my house, and a good number more around our property. They are easy to install, and wire. Then use the electrician to inspect your work, and hook them up to the main box after you have run all the wire and such.

I would definately do overhead, and not cut the concrete!