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 (
    251, 252, 253, 254, 256, 257, 258, 259, 
    260, 261, 262, 263, 264, 265, 266, 267, 
    268, 269, 270, 271, 272, 273, 274, 275, 
    276, 277, 278, 279, 280, 281, 282, 283, 
    284, 285, 286, 287, 288, 289, 290, 291, 
    292, 293, 294, 295, 296, 298, 299, 300
  ) 
  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 0.00092

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": 48,
      "filtered": 9.795915604,
      "index_condition": "cscart_product_prices.product_id in (251,252,253,254,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,289,290,291,292,293,294,295,296,298,299,300)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}

Result

product_id price
251 11000.00000000
252 0.00000000
253 48000.00000000
254 72540.00000000
256 42000.00000000
257 70000.00000000
258 48000.00000000
259 0.00000000
260 0.00000000
261 0.00000000
262 0.00000000
263 1560000.00000000
264 93600.00000000
265 0.00000000
266 69600.00000000
267 0.00000000
268 41289.00000000
269 0.00000000
270 0.00000000
271 0.00000000
272 0.00000000
273 0.00000000
274 0.00000000
275 0.00000000
276 0.00000000
277 38000.00000000
278 0.00000000
279 0.00000000
280 41289.00000000
281 66000.00000000
282 70000.00000000
283 70000.00000000
284 70000.00000000
285 66000.00000000
286 58800.00000000
287 30000.00000000
288 26400.00000000
289 60000.00000000
290 57000.00000000
291 105600.00000000
292 110000.00000000
293 0.00000000
294 231600.00000000
295 50400.00000000
296 32000.00000000
298 62000.00000000
299 37000.00000000
300 37000.00000000