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 (
    93322, 93321, 93320, 93319, 93318, 93307, 
    93306, 93304, 93223, 93189, 93095, 
    93009, 92836, 92462, 92450, 92448, 
    92447, 92434, 92433, 91822
  ) 
  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 0.00063

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
91822 1.69000000
92433 1.69000000
92434 1.69000000
92447 1.69000000
92448 1.69000000
92450 1.69000000
92462 1.69000000
92836 1.69000000
93009 1.69000000
93095 1.69000000
93189 1.69000000
93223 1.69000000
93304 1.69000000
93306 1.69000000
93307 1.69000000
93318 1.69000000
93319 1.69000000
93320 1.69000000
93321 1.69000000
93322 1.69000000