This is just a rough guess, but I think it might be around ... yen.
I can't say for sure exactly how much it will be, but I'm guessing it will be roughly ... yen.
ーThis is just a rough guess, but I think it might be around ... yen.
「概算だけど、だいたい…円になると思います。」
rough guess で「概算・だいたいの見当」という意味です。
ーI can't say for sure exactly how much it will be, but I'm guessing it will be roughly ... yen.
「はっきりいくらになるかは言えないですが、おおよそ…円くらいになるかと思います。」
I can't say for sure exactly how much it will be ...で「はっきりいくらになるかは言えない」
roughly で「おおよそ・概算で」
ご参考まで！
カナダ 
