I've been working for a client on several programming projects in the last few months. The client always paid regularly and left positive feedback for me on the platform I'm using to find work.
About one month ago the client proposed that I work for their company on a more regular basis and asked about my availability and hourly fees. I answered specifying an hourly fee that is consistent with market prices (albeit on the lower end). At that point I had realized that I had been working way below my minimum acceptable rate, not earning even enough to cover my business expenses (because I thought I had no other choice, because this is how it goes if one wants to get work on these international internet platforms, because I thought I would need the reputation, etc.). After my hourly fee disclosure I didn't hear from the client anymore and so I thought "oh well, they found someone else".
But now the client surprisingly contacted me again proposing that I work on some new projects. Exactly the same projects as before. The cooperation "on a more regular basis" wasn't mentioned anymore.
Now my question is: how can I charge more for exactly the same tasks that I performed a few months ago at a lower price? Note that on the platform I had always been paid per project and not per hour, so now having disclosed my hourly fees puts me in a weird position. The only strategy I've been able to come up with up to now is to tell the client I'm busy with something else and that I cannot take up any new projects. But that's not true; I need new contracts and I need the income.
So what should I do? Give up or negotiate (but I have no idea how)?