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 (
    1675, 1931, 1544, 1845, 1540, 1512, 1525, 
    1536, 1538, 1937, 1581, 1582, 1838, 
    1938, 1830, 1514, 1835, 1678, 1693, 
    1711, 1699, 1698, 1869, 1834, 1833, 
    1928, 1537, 1539, 1436, 1411, 1397, 
    1741, 1330, 1486, 1546, 1651, 1661, 
    255, 1742, 1598, 1565, 1597, 1708, 1694, 
    1732, 1596, 1632, 1618
  ) 
  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 0.00189

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_prices",
      "access_type": "range",
      "possible_keys": ["usergroup", "product_id", "lower_limit", "usergroup_id"],
      "key": "product_id",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 56,
      "filtered": 9.795915604,
      "index_condition": "cscart_product_prices.product_id in (1675,1931,1544,1845,1540,1512,1525,1536,1538,1937,1581,1582,1838,1938,1830,1514,1835,1678,1693,1711,1699,1698,1869,1834,1833,1928,1537,1539,1436,1411,1397,1741,1330,1486,1546,1651,1661,255,1742,1598,1565,1597,1708,1694,1732,1596,1632,1618)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}

Result

product_id price
255 66000.00000000
1330 122000.00000000
1397 34000.00000000
1411 22000.00000000
1436 22500.00000000
1486 118000.00000000
1512 28000.00000000
1514 34000.00000000
1525 28000.00000000
1536 45000.00000000
1537 30000.00000000
1538 48000.00000000
1539 32000.00000000
1540 42000.00000000
1544 28000.00000000
1546 10500.00000000
1565 22000.00000000
1581 0.00000000
1582 0.00000000
1596 128000.00000000
1597 23000.00000000
1598 23000.00000000
1618 0.00000000
1632 56000.00000000
1651 58000.00000000
1661 66000.00000000
1675 0.00000000
1678 39000.00000000
1693 35000.00000000
1694 0.00000000
1698 35000.00000000
1699 40000.00000000
1708 70000.00000000
1711 40000.00000000
1732 30000.00000000
1741 78000.00000000
1742 32000.00000000
1830 26000.00000000
1833 14000.00000000
1834 14000.00000000
1835 33000.00000000
1838 0.00000000
1845 33000.00000000
1869 28000.00000000
1928 23000.00000000
1931 23000.00000000
1937 23000.00000000
1938 22500.00000000