I have 5 years experience in Microsoft technologies and able to do this. Also I have exp in ASP 3.0 (classic asp), asp.net 1.1 and asp 2.0 with mssql 7.0 - 2005. I can able to commit the total time frame for this task after study the total dataflow of an application so my rates are 3$ / hrs. I have another issue with timings, I can only spent 20 hrs a week.
I haven't work with Paypal IPN, but i have idea about this.