This seems like a nice example of something we would call a Fermi problem in physics. Let me preface this by saying that as a physicist, I know little about the inner workings of the legal world, but here's my guess based on reading newspaper and blog accounts.
There seems to have been a two tiered approach, one fighting the recount in the courts and two fighting the recount on the ground at the county level. I think it's fair to assume that the Trump team focused its efforts in urban places where it perceived democrats could gain the most votes -- Milwaukee county in Wisconsin, Wayne, Macomb, and Oakland counties in Michigan. It seems like the court challenges in Pennsylvania succeeded, and so there was never a need to mount a ground effort in Philadelphia or Allegheny counties. I would guess that on order of ten attorneys were needed for each effort -- the court battle in Wisconsin, the court battle in Michigan, and the court battle in Pennsylvania. Then probably an additional ten attorneys were sent to each urban county. That's a total of 70 attorneys, working maybe full time for two weeks at conservatively $200 an hour.
So, my back of the envelope estimate is
70 attorneys x $200 per hour x 10 working days x 8 hours per day = $1 million
My error bars here are huge, but it seems to be the same order of magnitude that Stein was asked to spend by the states to get the recount effort started. I would be interested if anyone who knows more could make a better estimate.