Yes I love this rail, I purchased it the same time I purchased the TS55. I rip down a lot of sheets on site so this makes my day. I don't think I have ever clamped this rail down, it never moves...
The additional cost will not be a percentage of the price you paid for the rail, but rather an hourly rate for the time spent. Any decent machine shop should be able to do this for you in short order. As to pricing, you should expect to pay more for a single rail than if you were wanting multiple rails done. I would think the shop rate for an hour or two should cover a single rail -- multiple rails should be somewhat less per rail.