U$ 240 / month is not cheap, and I'd seriously consider an alternative or asking for a discount, but it's nowhere near the price of an office in Sao Paulo or Porto Alegre (I live in Uruguay and was looking for office space in Sao Paulo earlier this year).
If you have to pay for customers, then it's way too expensive.
I've seen a remote-based company put Slack to VERY good use, integrating it very tightly with their development process, I believe it definitely pays itself then.
If it's just a glorified IRC/XMPP, then definitely not.