I know I'm late here, but I figure I can mention it for reference...
I recently got a pair of boots (
these) taken in by a cobbler. The job cost me $80 and they took it in by the back seam. With the price of the boots plus cost of slimming, I spent about $230 all together, which isn't too unreasonable for a perfect-fitting pair of boots. The cobbler I used is located right on Wall Street (and I was too lazy to shop around

) so I'm pretty sure it'll be way cheaper anywhere else.
I definitely recommend going this route if you can't find anything that fits or you just really love a pair of boots that are too big in the calf.