$300 per month? You can finance and colocate big server for that price, as one of my customers does. $300 could also be used to rent 5-10 real servers in different countries, to run your own cloud with GeoIP and Linux containers. An other customer is running a shoutcast cluster of 6 hosts, two in US, 1 in Canada, two in Europe, and one in Korea for half that price. AWS traffic for such a shoutcast cluster would be several thousand $ per week.

Drop the stupid cloud. It costs to much. Rewrite your site to use only free software. Get a cheap Xen site. E.g. my own small server cost only €4 per month, offering 100mbit flat. Unfortunate my provider does no longer offer this contract, but there are other affordable hosts. Just take care, that you do not sign at a Virtuozzo/OpenVZ, or some cookie cutter provider who cripples performance like rackspace.

If unsure what Xen provider is good, get a real iron at Hetzner spot market for about €20-25, install a minimal Debian on with Linux containers, and run your site within a container. A real iron will likely provide more processing power then your site needs. So you can cross finance the host, by running applications you wrote for customer.

And always unbundle DNS contract from hosting contract, so you can switch fast, in case your hosting provider sucks.