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 (
    96572, 96559, 96114, 95928, 92920, 96615, 
    96498, 95750, 95749, 96567, 96499, 
    95897, 95896, 94823, 96556, 96522, 
    96521, 96520, 96519, 96518
  ) 
  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 0.00094

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
92920 1.69000000
94823 1.69000000
95749 1.69000000
95750 1.69000000
95896 1.69000000
95897 1.69000000
95928 1.69000000
96114 1.69000000
96498 1.69000000
96499 1.69000000
96518 1.69000000
96519 1.69000000
96520 1.69000000
96521 1.69000000
96522 1.69000000
96556 1.69000000
96559 1.69000000
96567 1.69000000
96572 1.69000000
96615 1.69000000