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 (
    1335, 1338, 1233, 1324, 1323, 1081, 1326, 
    1325, 1333, 1082, 1321, 1330, 1331, 
    1329, 1334, 1337, 1339, 1340, 1343, 
    399, 1299, 1810, 1811, 2918, 1341, 1342, 
    1856, 2913, 1815, 1819, 2914, 1859, 
    1858, 1850, 1294, 1298, 1297, 1293, 
    1295, 1814, 1816, 1817, 1818, 1820, 
    1821, 1822, 1823, 1824, 1825, 1826, 
    1827, 1828, 1829, 1830, 1831, 1300, 
    1301, 1302, 1304, 1303, 1812, 1808, 
    1807, 1813, 1836, 1860, 1861, 1837, 
    1851, 1853, 1838, 1839, 1840, 1841, 
    1842, 1843, 1844, 1845, 1846, 1847, 
    1848, 1849, 1855, 2915, 1857, 1862, 
    1835, 1834, 1863, 1809, 1864, 1150, 
    1152, 1149, 1151, 1148
  ) 
  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 0.00175

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.173824059,
    "filesort": {
      "sort_key": "cscart_product_prices.product_id",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_product_prices",
              "access_type": "ALL",
              "possible_keys": [
                "usergroup",
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "loops": 1,
              "rows": 810,
              "cost": 0.1445944,
              "filtered": 5.618655682,
              "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.product_id in (1335,1338,1233,1324,1323,1081,1326,1325,1333,1082,1321,1330,1331,1329,1334,1337,1339,1340,1343,399,1299,1810,1811,2918,1341,1342,1856,2913,1815,1819,2914,1859,1858,1850,1294,1298,1297,1293,1295,1814,1816,1817,1818,1820,1821,1822,1823,1824,1825,1826,1827,1828,1829,1830,1831,1300,1301,1302,1304,1303,1812,1808,1807,1813,1836,1860,1861,1837,1851,1853,1838,1839,1840,1841,1842,1843,1844,1845,1846,1847,1848,1849,1855,2915,1857,1862,1835,1834,1863,1809,1864,1150,1152,1149,1151,1148) and cscart_product_prices.usergroup_id in (0,1)"
            }
          }
        ]
      }
    }
  }
}