I'm sure it's pesos--I don't think any ATM machine will let you withdraw $7000 US
From what I've read banks such as Charles Schwab will reimburse most of the fees if you have enough money in your account. I also came across a web site that says HSBC will too but you have to pay $50/month for your checking account which sure won't work out for me. If I was to transfer some money to a bank in Mexico I would still have to pay some fees to get it transferred so it looks like, not matter what, you have to pay someone something unless you have a bunch of money in a Charles Schwab (or similar) account.
For me the bottom line is that for a two-week trip I may pay a little over $10 in ATM fees which I do not consider to be significant. If I start living in Mexico for longer periods of time then I'll need to make some changes.