Realistic costs in Mexico & Central America

[maysmor]

This is an incredibly broad and open to all opinion answers...

Ill be doing a tour from canada to central america, and I just dont know the costs of things will be once we get to Mexico and Central America.
We will be camping for most of the way (free as much as poss), cooking for ourselves (unless its really cheap), staying in budget places when not camping.
From experience, what are pples opinions on daily costs, or the costs for say 4 months. (not including bike, insurance) We will put aside whatever we need for the journey back, and probably just ride till we run out of money. We will be travelling on the british pounds, which is in our favour, but am I being too naive to think that those areas are dirt cheap still?
Cheers!