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 (
    94130, 94129, 92909, 94092, 94091, 94090, 
    94089, 94048, 93759, 93510, 93264, 
    93263, 93262, 93261, 93260, 93259, 
    93258, 89226, 93946, 93940
  ) 
  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 0.00077

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_prices range usergroup,product_id,lower_limit,usergroup_id usergroup 9 40 Using where

Result

product_id price
89226 1.69000000
92909 1.69000000
93258 1.69000000
93259 1.69000000
93260 1.69000000
93261 1.69000000
93262 1.69000000
93263 1.69000000
93264 1.69000000
93510 1.69000000
93759 1.69000000
93940 1.69000000
93946 1.69000000
94048 1.69000000
94089 1.69000000
94090 1.69000000
94091 1.69000000
94092 1.69000000
94129 1.69000000
94130 1.69000000