Presidential 1 Dollars MS-70

To call them rare would be a stretch...but you won't find one in a bag from the mint or in a roll of Presidential dollars. Also, if the "MS70" grade has been slapped on their by a basement grading company such as SEGS, then the grade is meaningless.

Any legitimate MS70 graded coins (and some would argue that a real MS70 coin doesn't exist) were plucked out of mint sets.

I don't see any reason for paying a premium to own a modern MS70 coin.

If you had a satin finish coin, then there is a much greater chance of a MS70 due to the care that is given with these coins and planchets. If you are talking about a regular strike coin, then MS70 would be a very, very rare conditional coin.