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 (
    60624, 60623, 60622, 60621, 60620, 60619, 
    60618, 77578, 77577, 77576, 77575, 
    77574, 77573, 77572, 77571, 77570, 
    77569, 77568, 77567, 77566
  ) 
  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 0.00082

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
60618 1.69000000
60619 1.69000000
60620 1.69000000
60621 1.69000000
60622 1.69000000
60623 1.69000000
60624 1.69000000
77566 1.69000000
77567 1.69000000
77568 1.69000000
77569 1.69000000
77570 1.69000000
77571 1.69000000
77572 1.69000000
77573 1.69000000
77574 1.69000000
77575 1.69000000
77576 1.69000000
77577 1.69000000
77578 8.99000000