Hello Sir,
I am interested in your project and can complete it well as per your description. As for open source, do you have any names in your mind for helpdesk or dashboard etc. Let me know full details and I will give you 100% result for the output. Having 6+ experience in asp.net. I am also familiar with many payment gateways like, paypal, google checkout etc. And also knowledge of javascript, jquery, ajax, css, html etc.
If you think, my bid is higher, then just give me code of your site and I will give you free of cost suggestions about sql injection, optimization of code, performance and testing of website, free of cost and suggest you which area need to improvement. After that you can hire me for those fixings or someone else who can do those in lower amount then what I have bid. Hope to work with you for long term.