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 (
    102182, 102181, 101847, 101846, 101845, 
    101844, 101843, 101826, 101825, 101812, 
    101811, 101810, 101707, 101706, 101472, 
    101961, 101699, 101403, 101402, 101401
  ) 
  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 0.00067

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
101401 1.69000000
101402 1.69000000
101403 1.69000000
101472 1.69000000
101699 1.69000000
101706 1.69000000
101707 1.69000000
101810 1.69000000
101811 1.69000000
101812 1.69000000
101825 1.69000000
101826 1.69000000
101843 1.69000000
101844 1.69000000
101845 1.69000000
101846 1.69000000
101847 1.69000000
101961 1.69000000
102181 1.69000000
102182 1.69000000