I think it´s at least slang, isn`t it? I would have written something like this:

"Hello ChoiJ

Thanks very much for your offer. I`m afraid that I can`t pay you that much money because I`m a student. I`m very sorry, but we can`t work together.
I already found another modeler, Blattsalat from the Acknex forums, who makes me the model for a price that I`m able to pay.
Nevertheless I wish you all the best. Your business is great for people who are able to pay more than me. I´m sure you will find another job.

Thanks again,
Liam"

Maybe not the best English, too. But I think it`s understandable and more friendly.