Sparrow,
Not sure if you are concerned with the structural integrity or the height of your transom (or both).
This is what some of us have used in the past with much satisfaction when we had 20" transoms:
http://www.bobsmachine.com/
manual jack plate #MJ5
I would not however recommend this if you have doubts about the structural integrity of your existing setup. Again, try to have an expert take a look if that's the case.
That price seems to be in the ballpark. 4 Days? Sure, but it took me about 4 months of planning!