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 (
    94340, 95201, 94314, 94294, 94293, 94292, 
    94290, 94289, 94288, 94287, 94258, 
    94257, 94250, 94249, 94248, 94247, 
    94246, 94245, 94244, 94243, 94242, 
    94241, 94240, 94239, 94238, 94237, 
    94236, 94235, 94234, 94233, 94232, 
    94229, 94228, 94224, 94223, 94222, 
    94221, 94220, 94219, 94218
  ) 
  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 0.00088

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 usergroup 9 80 Using where

Result

product_id price
94218 1.69000000
94219 1.69000000
94220 1.69000000
94221 1.69000000
94222 1.69000000
94223 1.69000000
94224 1.69000000
94228 1.69000000
94229 1.69000000
94232 1.69000000
94233 1.69000000
94234 1.69000000
94235 1.69000000
94236 1.69000000
94237 1.69000000
94238 1.69000000
94239 1.69000000
94240 1.69000000
94241 1.69000000
94242 1.69000000
94243 1.69000000
94244 1.69000000
94245 1.69000000
94246 1.69000000
94247 1.69000000
94248 1.69000000
94249 1.69000000
94250 1.69000000
94257 1.69000000
94258 1.69000000
94287 1.69000000
94288 1.69000000
94289 1.69000000
94290 1.69000000
94292 1.69000000
94293 1.69000000
94294 1.69000000
94314 1.69000000
94340 1.69000000
95201 1.69000000