MPG's will vary by driving style, city vs. highway, location (flat or hilly), specific tire selection etc but it seems to drop to around 15mpgs +/- 2mpg with 2-3" lift and larger tires. Just ball parking here as my 4Runner has not even arrived.
On pricing I cannot really help you but there is a "how much did you pay thread" that will come up using the search function that has pages and pages of prices. Take them with a grain of salt as I found in my area (Michigan) dealers were much tougher/reluctant to negotiate as much as others were saying they got and walked out on a couple deals before realizing that I was going to pay ~1500 more than most were able to get in other regions. Not sure how your market is but don’t get discourage if you see "low" prices posted as every state and situation is different, sales tax, sales tax reduction for trade in etc, do your homework, figure out what you are willing to pay and go from there. It might be worth a trip to another part of the country, depends on what your time is worth and how far it is.
As that price does not include dealer fees, sales tax, document fees etc I don’t think it’s much of a stretch for me to say it is overpriced for an SR5….but again I didn’t do the homework
As a general rule of thumb you almost always over pay for dealer installed options, most likely even more then what it would cost you to purchase them and pay a 3rd party mechanic to install them. I would ask the dealer for a breakdown of the exact parts on the truck and then price them yourself and determine the markup. As a guess the mark up is not something I would be willing to swallow, however my skills, time , family life etc is far different from yours and I can’t not make that call for you.
Just remember while sometimes hard to find these are not rare vehicles (I had one dealer tell me the price was justified because I was not guaranteed I could get what I wanted, they had one identical to the one I ordered on the lot.....I told her it was a Toyota , not a Ferrari)
Best of luck, and even if you are dead set on those Mods spend an hour looking around the build pages here to get some ideas of what people do to their trucks might change your mind on what you want.