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 (
    92499, 92498, 92486, 91950, 91930, 91909, 
    1417, 92477, 91779, 91778, 91777, 91776, 
    91775, 91774, 91773, 91772, 91771, 
    91770, 91769, 91768
  ) 
  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 0.00087

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
1417 1.69000000
91768 1.69000000
91769 1.69000000
91770 1.69000000
91771 1.69000000
91772 1.69000000
91773 1.69000000
91774 1.69000000
91775 1.69000000
91776 1.69000000
91777 1.69000000
91778 1.69000000
91779 1.69000000
91909 1.69000000
91930 1.69000000
91950 1.69000000
92477 1.69000000
92486 1.69000000
92498 1.69000000
92499 1.69000000