Since it's only xx yen, why don't you use your own money to buy it instead of using someone else's credit card??
この場合、次のような言い方ができますよ。
ーSince it's only xx yen, why don't you use your own money to buy it instead of using someone else's credit card?
「XX円くらいなら自分の金使って買えよ。人のクレジットカード使ってんじゃねーよ」
to use your own money to buy ... で「自分のお金で…を買う」
to use someone else's credit card で「誰かのクレジットカードを使う」
ご参考まで！
カナダ 
