Alright, I think I may have something here:
$sppc_query = "select p.products_id, p.products_model, pd.products_name, pg.customers_group_id, pg.customer_group_price from " . TABLE_PRODUCTS . " p, " . TABLE_PRODUCTS_DESCRIPTION . " pd, " . TABLE_PRODUCTS_GROUPS . " pg where p.products_id = pd.products_id and p.products_id = pg.products_id and pg.customers_group_id = " . $customer_group_id . " order by p.products_model";
This seems to return all of the correct information in phpMyAdmin.
Am I on the right track with this?