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 (
    93232, 1645, 93574, 93526, 93067, 93064, 
    93063, 93003, 93002, 93001, 93000, 
    92999, 92998, 92997, 92996, 92995, 
    92994, 92993, 92992, 92991
  ) 
  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 0.00068

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
1645 1.69000000
92991 1.69000000
92992 1.69000000
92993 1.69000000
92994 1.69000000
92995 1.69000000
92996 1.69000000
92997 1.69000000
92998 1.69000000
92999 1.69000000
93000 1.69000000
93001 1.69000000
93002 1.69000000
93003 1.69000000
93063 1.69000000
93064 1.69000000
93067 1.69000000
93232 1.69000000
93526 1.69000000
93574 1.69000000