Its been a while, but I think you could just do
DIM variablenamehere as String??
*My edit
If you were to set up each variable to be strictly numeric/alphabetic, for numeric, just do
Dim variablename as single/double (whichever fits your need, if its a price, single might be sufficient, might not, think it only goes up to 32,000 something)
And for the alphabetic, just use the "as String" I think
Could be off though
Jeff