we see them a fair amount on Bullseye pistols.. They work great but the gun has to be kept clean... not something I'd do for a carry pistol.. think the cost is around $200
depending upon how sloppy the slide fit is there are some ways to tighten the slide fit.. slide can be compressed but it takes someone who has a lot of experience with the process. frame rails can be welded up and re-cut to fit better.. we do this quite a bit on BE guns but only on steel frames, but I see no reason this couldn't be done on aluminum by a good tig welder..
a gunsmith fit barrel will take up some of the slack at lockup.
with all that said.. not sure it's worth the cost.