Count occurnence of a Letter and number string in a single cell

First off apologies for the subject line!

Example:

My Cell contains this

O622, Z370, O48X, O680, O700, O679, O681, O418, O268, R030, R80X, G35X, E668, Z833

To count if I have an occurrence of an R code in the range of R00-R99 I use this formula

=SUMPRODUCT(--ISNUMBER(SEARCH("r",G3)))

I do not know how to count if I have an instance of this range A00-B99

Thanks

Linda