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 (
    38067, 38037, 38036, 38034, 38033, 38032, 
    38031, 38030, 38029, 38028, 38027, 
    38026, 38025, 38022, 38021, 38020, 
    38019, 38018, 38017, 38016, 38015, 
    38014, 38013, 38012, 38011, 38010, 
    38009, 38008, 38007, 38006, 38005, 
    38004, 38003, 38002, 38001, 38000, 
    37999, 37998, 37997, 37996, 37995, 
    37994, 37993, 37992, 37991, 37990, 
    37989, 40283, 38872, 38159, 79896, 
    38226, 38078, 38077, 38076, 37988, 
    37987, 37986, 38458, 38423, 38422, 
    38421, 38420, 38419, 38418, 38417, 
    38400, 38399, 38244, 38227, 38172, 
    37985, 40512, 38181, 38180, 40355, 
    38884, 38062, 38043, 38042
  ) 
  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 0.00290

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 9 160 Using where

Result

product_id price
37985 1.69000000
37986 1.69000000
37987 1.69000000
37988 1.69000000
37989 1.69000000
37990 1.69000000
37991 1.69000000
37992 1.69000000
37993 1.69000000
37994 1.69000000
37995 1.69000000
37996 1.69000000
37997 1.69000000
37998 1.69000000
37999 1.69000000
38000 1.69000000
38001 1.69000000
38002 1.69000000
38003 1.69000000
38004 1.69000000
38005 1.69000000
38006 1.69000000
38007 1.69000000
38008 1.69000000
38009 1.69000000
38010 1.69000000
38011 1.69000000
38012 1.69000000
38013 1.69000000
38014 1.69000000
38015 1.69000000
38016 1.69000000
38017 1.69000000
38018 1.69000000
38019 1.69000000
38020 1.69000000
38021 1.69000000
38022 1.69000000
38025 1.69000000
38026 1.69000000
38027 1.69000000
38028 1.69000000
38029 1.69000000
38030 1.69000000
38031 1.69000000
38032 1.69000000
38033 1.69000000
38034 1.69000000
38036 1.69000000
38037 1.69000000
38042 1.69000000
38043 1.69000000
38062 1.69000000
38067 1.69000000
38076 1.69000000
38077 1.69000000
38078 1.69000000
38159 1.69000000
38172 1.69000000
38180 1.69000000
38181 1.69000000
38226 1.69000000
38227 1.69000000
38244 1.69000000
38399 1.69000000
38400 1.69000000
38417 1.69000000
38418 1.69000000
38419 1.69000000
38420 1.69000000
38421 1.69000000
38422 1.69000000
38423 1.69000000
38458 1.69000000
38872 1.69000000
38884 1.69000000
40283 1.69000000
40355 1.69000000
40512 1.69000000
79896 1.69000000