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 (
    96593, 96592, 96591, 96590, 96589, 97405, 
    96929, 96736, 96616, 94871, 97239, 
    97237, 96984, 96622, 97235, 97234, 
    97213, 97177, 97176, 97175
  ) 
  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 0.00083

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 40 Using where

Result

product_id price
94871 1.69000000
96589 1.69000000
96590 1.69000000
96591 1.69000000
96592 1.69000000
96593 1.69000000
96616 1.69000000
96622 1.69000000
96736 1.69000000
96929 1.69000000
96984 1.69000000
97175 1.69000000
97176 1.69000000
97177 1.69000000
97213 1.69000000
97234 1.69000000
97235 1.69000000
97237 1.69000000
97239 1.69000000
97405 1.69000000