There are two alternatives to shortening the barrel - opening the choke with a choke reamer to a skeet choke; or having the choke section machined for a set of choke tubes.
I would simply buy a short (26"), open-choke barrel at a gun show - where I see them quite often F/S in the $75 range.
You could sell your 30" barrel to one of the gun show parts guys, and recoup most of your cost, if not be able to swap outright.