Or, add a function into the query. In the query table the field would be something like:
My Final Price: iif([My Price] = 0, Null, [My Price])
This would be OK for smaller reports. If you are pulling large data sets from a linked SQL Server, the MSAccess iif function in an Access SQL Statement can not be converted into TSQL and it will not run efficiently.
Another way would be to pull the data into a temp table - then top it off by running a update query against the temp table.
If the data only goes to a report, the solution above looks pretty good.