With constant care for details
I guess that it can be done on $60 per day, if you watch very carefully all the time and don't waste money anywhere. Hopefully, you mean $60 per day each. If it is $60 per day for the both of you, then I think that is a little too tight -- figuring 350 miles per day, less than $30 for gas if prices don't go up too much between now and then. Camping expenses up to $20 per day (often can be done free or more cheaply) and food at $15 per day if you are careful. I think no question, being frugal, you could do it on 2X $60. You do need to have an emergency fund set aside though, or you run the risk of getting stuck somewhere.