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 (
    92910, 92680, 94278, 94277, 94276, 94207, 
    94191, 94140, 93939, 93932, 93760, 
    93525, 93451, 93346, 94187, 94185, 
    94184, 94183, 93378, 94141
  ) 
  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 0.00075

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
92680 1.69000000
92910 1.69000000
93346 1.69000000
93378 1.69000000
93451 1.69000000
93525 1.69000000
93760 1.69000000
93932 1.69000000
93939 1.69000000
94140 1.69000000
94141 1.69000000
94183 1.69000000
94184 1.69000000
94185 1.69000000
94187 1.69000000
94191 1.69000000
94207 1.69000000
94276 1.69000000
94277 1.69000000
94278 1.69000000