Haven't actually validated the cells and formulae (probably needs doing as, for example, 'Florida - OFT'!C6 <> 'Florida - OFT'!C5 and I suspect it should be equal) but a large omission could be sales tax in the states. A small omission would be examples like paying for an FAA medical in the states in order to solo. Are you sure a bike is all you need when in the States? How about transport in the UK, that has a cost. If you have made the decision to drill down to the nearest $25 then you should probably work out food costs more exactly.
Also add 20% contingency.
Quite right about the validation.
I'll add a medical ($100) into the calculations.
The bike is probably uneccessary as you say the costs are so small. I've ignored food as its going to be a cost wherever i go (though probably not the same).
What is the rate of sales tax in Florida?
Does it get added to the cost of every lesson or is it just on goods purchased?