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 (
    1401, 1402, 1403, 1384, 727, 729, 726, 
    1583, 251, 237, 238, 373, 372, 339, 365, 
    236, 786, 381, 389, 1914, 1321, 1368, 
    1877, 1876, 1878, 1806, 1794, 1807, 
    1884, 1886, 1889, 1890, 1881, 1879, 
    1880, 1882, 1888, 1871, 1887, 715, 714, 
    1485, 1915, 345, 1451, 1183, 18, 17, 
    19, 1814, 1813, 1874, 1875, 974, 1574, 
    1575, 1812, 1811, 1507, 1853, 1856, 
    1918, 1919, 1862, 1861, 1857, 1883, 
    1860, 1859, 1854, 1923, 1858, 1922, 
    1855, 1920, 1469, 344, 1850, 1551, 284, 
    1475, 1276, 1569, 1198, 1179, 1281, 
    926, 1258, 1168, 1394, 1259, 1865, 390, 
    1204, 1864, 1863
  ) 
  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 0.00296

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": 100,
      "filtered": 19.59183121,
      "index_condition": "cscart_product_prices.product_id in (1401,1402,1403,1384,727,729,726,1583,251,237,238,373,372,339,365,236,786,381,389,1914,1321,1368,1877,1876,1878,1806,1794,1807,1884,1886,1889,1890,1881,1879,1880,1882,1888,1871,1887,715,714,1485,1915,345,1451,1183,18,17,19,1814,1813,1874,1875,974,1574,1575,1812,1811,1507,1853,1856,1918,1919,1862,1861,1857,1883,1860,1859,1854,1923,1858,1922,1855,1920,1469,344,1850,1551,284,1475,1276,1569,1198,1179,1281,926,1258,1168,1394,1259,1865,390,1204,1864,1863)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}

Result

product_id price
17 22500.00000000
18 22500.00000000
19 22500.00000000
236 35000.00000000
237 35000.00000000
238 34000.00000000
251 11000.00000000
284 70000.00000000
339 0.00000000
344 34000.00000000
345 34000.00000000
365 33000.00000000
372 35000.00000000
373 35000.00000000
381 33000.00000000
389 34000.00000000
390 7000.00000000
714 22000.00000000
715 27000.00000000
726 28000.00000000
727 43000.00000000
729 42000.00000000
786 0.00000000
926 235000.00000000
974 56000.00000000
1168 32000.00000000
1179 260000.00000000
1183 38000.00000000
1198 30000.00000000
1204 21000.00000000
1258 29000.00000000
1259 30000.00000000
1276 0.00000000
1281 32000.00000000
1321 20000.00000000
1368 20000.00000000
1384 55000.00000000
1394 31000.00000000
1401 55000.00000000
1402 55000.00000000
1403 55000.00000000
1451 37000.00000000
1469 28000.00000000
1475 0.00000000
1485 22000.00000000
1507 130000.00000000
1551 70000.00000000
1569 68500.00000000
1574 30000.00000000
1575 30000.00000000
1583 12000.00000000
1794 5000.00000000
1806 5000.00000000
1807 5000.00000000
1811 24000.00000000
1812 24000.00000000
1813 25000.00000000
1814 25000.00000000
1850 50000.00000000
1853 46000.00000000
1854 46000.00000000
1855 46000.00000000
1856 50000.00000000
1857 50000.00000000
1858 23500.00000000
1859 23500.00000000
1860 23500.00000000
1861 23500.00000000
1862 23500.00000000
1863 33000.00000000
1864 32000.00000000
1865 45000.00000000
1871 48000.00000000
1874 65000.00000000
1875 65000.00000000
1876 44000.00000000
1877 44000.00000000
1878 44000.00000000
1879 44000.00000000
1880 44000.00000000
1881 44000.00000000
1882 48000.00000000
1883 30000.00000000
1884 48000.00000000
1886 48000.00000000
1887 48000.00000000
1888 48000.00000000
1889 48000.00000000
1890 48000.00000000
1914 55000.00000000
1915 72000.00000000
1918 13000.00000000
1919 23500.00000000
1920 23500.00000000
1922 22500.00000000
1923 46000.00000000