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 (
    92533, 92532, 93007, 98607, 92736, 92513, 
    92806, 92805, 92473, 92830, 92829, 
    92276, 92612, 92663, 92118, 98608, 
    92778, 92777, 92776, 92775
  ) 
  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 0.00069

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
92118 1.69000000
92276 1.69000000
92473 1.69000000
92513 1.69000000
92532 1.69000000
92533 1.69000000
92612 1.69000000
92663 1.69000000
92736 1.69000000
92775 1.69000000
92776 1.69000000
92777 1.69000000
92778 1.69000000
92805 1.69000000
92806 1.69000000
92829 1.69000000
92830 1.69000000
93007 1.69000000
98607 1.69000000
98608 1.69000000