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 (
    106778, 106777, 106776, 106775, 106774, 
    106313, 106760, 106759, 106369, 106368, 
    106273, 106271, 106270, 106269, 106260, 
    106243, 106242, 106241, 106240, 106239
  ) 
  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 0.00054

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
106239 1.69000000
106240 1.69000000
106241 1.69000000
106242 1.69000000
106243 1.69000000
106260 1.69000000
106269 1.69000000
106270 1.69000000
106271 1.69000000
106273 1.69000000
106313 1.69000000
106368 1.69000000
106369 1.69000000
106759 1.69000000
106760 1.69000000
106774 1.69000000
106775 1.69000000
106776 1.69000000
106777 1.69000000
106778 1.69000000