Set up a Product with the Attributes and Prices manually ...
Browse, via phpMyAdmin, the products_attributes table and look for the values in:
options_id
options_values_id
Once you can identify the Option Name and Option Value, you could run a SQL command to update the prices ...
Backup your database before attempting this or you will be doomed ... 
Code:
UPDATE products_attributes SET options_values_price = XX.XX WHERE options_id = YY and options_values_id = ZZ;
where XX.XX is the Price for the Attribute and YY is the Option Name (options_id) for Size and ZZ is the Option Value (options_values_id) for Small ...