Hi,
Freelancer provide a REST API that you can query for new jobs, and also post bids etc. So you would just need something that connects to this API every X minutes, searches for new projects that meet your specific criteria and then send out the bid with your desired text.
I would propose either a C# windows service or simple WinForms interface to do this for you. You just leave it running when you want it, and it does the rest.
If you're happy to discuss further, please message me.
Thanks,
Chris