My situation is this.

I coded in php and built a facebook app. After 3 days it has 13,000 users.

I have my own server at hostmonster. It is a regular plan costing me about $70 per year. It has unlimited bandwidth.

I did not anticipate hosting apps or that it could pick up so many users.

Already 1 Gb of data was transferred in the last few days.

I am planning to build a few more apps(around 10 - 20) and reach atleast a million users in total.

Should I continue hosting on the same server or move to a VPS? I am a student and I don't have too much of a disposable income. So I want to move only if it is necessary.

Right now it shows 1 Gb/infinity in data transfer.

Any help/suggestions highly appreciated.