SELECT 
  cscart_product_prices.product_id, 
  MIN(
    IF(
      cscart_product_prices.percentage_discount = 0, 
      cscart_product_prices.price, 
      cscart_product_prices.price - (
        cscart_product_prices.price * cscart_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  cscart_product_prices 
WHERE 
  cscart_product_prices.product_id IN (
    172, 168, 167, 169, 175, 246, 173, 161, 
    165, 166, 163, 164
  ) 
  AND cscart_product_prices.lower_limit = 1 
  AND cscart_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  cscart_product_prices.product_id

Query time 0.00040

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_prices range usergroup,product_id,lower_limit,usergroup_id product_id 3 17 Using index condition; Using where

Result

product_id price
161 279.99000000
163 899.99000000
164 249.99000000
165 599.95000000
166 749.95000000
167 549.95000000
168 1.00000000
169 749.95000000
172 299.99000000
173 349.99000000
175 179.99000000
246 399.99000000