Since the sizes are the same for each product and don't change, there is no need for the complex join query for the rsSize recordset.
the rsSize recordset can just be:
SELECT * FROM options
Will the sizes effect the product price? if not, there is no need for the rsSizePrice Lookup recordset.
In the select list, you can just use the option name column for both the ID and the Label.
to hide the select list if the category is not AG Clothing, use a show region behavior. Select the size list in design view. In the Server behaviors panel, click the plus button and select Webassist -> Utilities -> Show Region Utility.
For the IF, click the plus button and select the ProductCategory from the WADAProducts recordset. Set "Is" to "=". for the value enter "AG Clothing"