1 sale = 1 price

2 sales at different prices = range

you use key prices of the day of the transaction

transaction was on July 18th and sold for 800 usd

key prices that day where 1.71 usd

800/1.71 = 467.83 keys

via rules you can round to the nearest 10 keys but must be rounded for the nearest key

https://forums.backpack.tf/topic/6033-rules-for-unusual-price-suggestions/

thats 470 or 468 keys

you need to resuggest

personally I would just do 470 keys flat