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 (
    73215, 73214, 73213, 73212, 73211, 73210, 
    73209, 73208, 73207, 73206, 73205, 
    73204, 73203, 73202, 73201, 73200, 
    73199, 73198, 73197, 73196, 73195
  ) 
  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 0.00055

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 42 Using where

Result

product_id price
73195 1.69000000
73196 1.69000000
73197 1.69000000
73198 1.69000000
73199 1.69000000
73200 1.69000000
73201 1.69000000
73202 1.69000000
73203 1.69000000
73204 1.69000000
73205 1.69000000
73206 1.69000000
73207 1.69000000
73208 1.69000000
73209 1.69000000
73210 1.69000000
73211 1.69000000
73212 1.69000000
73213 1.69000000
73214 1.69000000
73215 1.69000000