For an average per day cost think in the area of $65 US , and that includes all expenses, insurance , food , fuel and economical hotels, border fees , bike maintenance. Of course you can drive that figure up to any value if you don't mind the pennies by staying at the overpriced international chain hotels and super deluxe hotels and snooty restaurants favoured by the millionaires.
For $65 you will be eating well enough to gain weigt if you are not careful.
Just make sure you have adequate funds in your bank account so you can extract cash from bank machines as needed in each country. If ther e is any possibility that you are going to run out of money by the time you hit Nicaragua you are either living really beyond your means or you had no business setting out on such a trip in the first place. But you definitely do not need to be super rich to do a good trip like this.
Ten days from the time you cross into Mexico is possible , but you will have to clip along at a steady rate, no hanging about in any special spots you might discover.
Expanding on Marior97 's comment about eating at "gas stations" I think this may be referring to the newer PEMEX stations which often incorporate an OXXO convenience store , or a 7-11 store , or a SIX store or any of a number of different names. They all offer good sterile packed prepared sandwiches, burritos, hot dogs and fresh coffe- good for cheap and fast breakfast. Beyond Mexico you will get simmilar fare at the ESSO, TEXACO ,SHELL gas stations with their c-stores too.

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93