Thank You for writing into AskPatty!! Such repair, can vary in cost depending on hourly labor rates, and mark-up of parts. Typically, this can cost more at a dealership than an independent garage. I recommend that you call around for quotes to a number of trusted facilities to have more of an idea in your market.
Hope this Helps
A. J. Valle
According to the CarMD Vehicle Health Index (http://corp.carmd.com) this type of repair varies greatly by year, make, model and whether you're having it done professionally or not. "Replace Manifold Gasket" is actually a fairly common repair in the top 10 last year, at an average cost of $338 for parts and labor. To have the transmission oil, filter and gasket all changed averages about $483.
〉 Answered on Jul 16th, 2012 by Kristin Brocoff, Director of Corporate Communications at CarMD.com
Check www.repairpal.com they give pricing based on the area you live. Here's a pretty good article as well about transmission fluid changes.
〉 Answered on Jul 16th, 2012 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines