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 (
    92048, 92047, 92046, 92045, 92044, 92043, 
    92042, 92041, 92040, 92039, 92038, 
    92037, 92036, 92035, 92034, 92033, 
    92032, 92031, 91994, 91786
  ) 
  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 0.00049

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
91786 1.69000000
91994 1.69000000
92031 1.69000000
92032 1.69000000
92033 1.69000000
92034 1.69000000
92035 1.69000000
92036 1.69000000
92037 1.69000000
92038 1.69000000
92039 1.69000000
92040 1.69000000
92041 1.69000000
92042 1.69000000
92043 1.69000000
92044 1.69000000
92045 1.69000000
92046 1.69000000
92047 1.69000000
92048 1.69000000