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 (
    108922, 97567, 98182, 108918, 97536, 
    97674, 97673, 97551, 97508, 109006, 
    97467, 97466, 97711, 97710, 97700, 
    97699, 97289, 97287, 97279, 97531
  ) 
  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 0.00061

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
97279 1.69000000
97287 1.69000000
97289 1.69000000
97466 1.69000000
97467 1.69000000
97508 1.69000000
97531 1.69000000
97536 1.69000000
97551 1.69000000
97567 1.69000000
97673 1.69000000
97674 1.69000000
97699 1.69000000
97700 1.69000000
97710 1.69000000
97711 1.69000000
98182 1.69000000
108918 1.69000000
108922 1.69000000
109006 1.69000000