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 (
    1820, 1897, 1760, 1807, 1847, 2363, 1816, 
    1819, 1849, 1802, 1801, 1880, 1855, 
    1808, 1891, 1892, 1821, 2164, 1786, 
    1805, 1822, 2170, 1861, 1856, 1846, 
    1885, 1873, 1824, 1869, 2361, 1825, 
    1826, 1749, 1752, 1827, 1870, 1803, 
    1828, 1754, 1770, 1879, 1874, 1829, 
    1864, 1904, 1842, 1781, 1894, 2153, 
    1886, 1887, 1746, 1753, 1875, 1830, 
    1863, 1852, 1906, 1757, 1895, 1800, 
    1848, 1977, 1832, 1765, 1768, 1769, 
    1835, 1871, 1838, 1766, 1903, 1773, 
    1762, 1763
  ) 
  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 0.00076

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "53.86"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "product_id",
        "used_key_parts": [
          "product_id"
        ],
        "key_length": "3",
        "rows_examined_per_scan": 78,
        "rows_produced_per_join": 15,
        "filtered": "19.97",
        "index_condition": "(`cscartdevel`.`cscart_product_prices`.`product_id` in (1820,1897,1760,1807,1847,2363,1816,1819,1849,1802,1801,1880,1855,1808,1891,1892,1821,2164,1786,1805,1822,2170,1861,1856,1846,1885,1873,1824,1869,2361,1825,1826,1749,1752,1827,1870,1803,1828,1754,1770,1879,1874,1829,1864,1904,1842,1781,1894,2153,1886,1887,1746,1753,1875,1830,1863,1852,1906,1757,1895,1800,1848,1977,1832,1765,1768,1769,1835,1871,1838,1766,1903,1773,1762,1763))",
        "cost_info": {
          "read_cost": "52.30",
          "eval_cost": "1.56",
          "prefix_cost": "53.86",
          "data_read_per_join": "373"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`cscartdevel`.`cscart_product_prices`.`lower_limit` = 1) and (`cscartdevel`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}