I have a leaking brake on the left rear driver wheel. I was advised I need a new break line. I was advised it would cost anywhere from $1800 to $3000. I was advised they had to drop the gas tank, frame, etc. Could it really cost this much?

Get another estimate from a different repair facility!

Agree with Pushrod. Just to add some clarity here, replacing a "brake line" is something that is labor intensive, especially on a 16 year old vehicle which likely has significant cumulative corrosion from Minnesota winters. The line will have to be fabricated and shaped to your vehicle, cut to the proper length, and then installed in one piece. This is why removal of components may be required -- because to put the line through to where it belongs, there will be required access. If you get a competitive quote, perhaps you'll have some flexibility with prospective shops near you. Good luck.