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 (
    94652, 94651, 94650, 94649, 94648, 94647, 
    94646, 94645, 94644, 94643, 94642, 
    94641, 94640, 94639, 94638, 94637, 
    94636, 94635, 94634, 94633
  ) 
  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 0.00071

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
94633 1.69000000
94634 1.69000000
94635 1.69000000
94636 1.69000000
94637 1.69000000
94638 1.69000000
94639 1.69000000
94640 1.69000000
94641 1.69000000
94642 1.69000000
94643 1.69000000
94644 1.69000000
94645 1.69000000
94646 1.69000000
94647 1.69000000
94648 1.69000000
94649 1.69000000
94650 1.69000000
94651 1.69000000
94652 1.69000000