typically for paypal, we use a different number than what marketplace uses. You'd have to find out what keys were selling for around the time on this forum:

https://forums.backpack.tf/forum/27-team-fortress-2-cash-trading/

From what I gathered, this is what they were going for:

Buying:

$1.61 - https://forums.backpack.tf/topic/85893-%F0%9F%8C%BBbuying-keys-161-usd-backpacks-via-paypal-%E2%9C%94%EF%B8%8F300-trust-ratings%F0%9F%8C%BB/

$1.58 - https://forums.backpack.tf/topic/84273-gameygame6-is-buying-backpacks-and-keys-158-paypal-22-cad-etransfer-with-10000-cash-90-trust-70k-inventory/

$1.54 - https://forums.backpack.tf/topic/76871-buying-keys-154-each-buying-backpacks-ref-tools-all-items-paypal-250-trust/

Selling:

$1.62 - https://forums.backpack.tf/topic/38399-%F0%9F%94%A5frost-is-selling-keys-for-162-crypto-stock-1000-keys-1000-trust-ratings%E2%9C%85-accepting-all-coins-on-all-networks-free-transactions-for-binance-pay/

$1.65 - https://forums.backpack.tf/topic/76949-selling-keys-165-for-crypto-zelle-venmo-cash-app-wise-payoneer-no-paypal-333-rep/

$1.68 - https://forums.backpack.tf/topic/86001-%E2%9A%A0%EF%B8%8F-%F0%9D%90%92%F0%9D%90%9E%F0%9D%90%A5%F0%9D%90%A5%F0%9D%90%A2%F0%9D%90%A7%F0%9D%90%A0-%F0%9D%90%8A%F0%9D%90%9E%F0%9D%90%B2%F0%9D%90%AC-%F0%9D%9F%8F%F0%9D%9F%94%F0%9D%9F%96-%F0%9D%90%94%F0%9D%90%92%F0%9D%90%83-%F0%9D%90%AF%F0%9D%90%A2%F0%9D%90%9A-%F0%9D%90%8F%F0%9D%90%9A%F0%9D%90%B2%F0%9D%90%8F%F0%9D%90%9A%F0%9D%90%A5-%F0%9D%9F%92-%F0%9D%90%91%F0%9D%90%9A%F0%9D%90%A7%F0%9D%90%A4%F0%9D%90%9E%F0%9D%90%9D-%F0%9D%90%81%F0%9D%90%9A%F0%9D%90%9C%F0%9D%90%A4%F0%9D%90%A9%F0%9D%90%9A%F0%9D%90%9C%F0%9D%90%A4-%F0%9D%9F%8F%F0%9D%9F%8E%F0%9D%9F%8E%F0%9D%9F%8E%F0%9D%9F%8E%F0%9D%9F%8E%F0%9D%9F%8E-%F0%9D%90%93%F0%9D%90%AB%F0%9D%90%9A%F0%9D%90%A7%F0%9D%90%AC%F0%9D%90%9A%F0%9D%90%9C%F0%9D%90%AD%F0%9D%90%9E%F0%9D%90%9D-%E2%9A%A0%EF%B8%8F/

Which brings the average price of keys ~$1.61 for PayPal transfers, meaning the sale is more accurate to

$252.49 / 1.61 = ~156.83 keys

^using the value paid

Should round to 157 keys for the suggestion, nearest whole key since cash can be considered pure.