Hi,
I have recently developed a high quality custom browser in C#. That project was for about $500, however, since I already have the source code, I can modify it according to your needs and give it to you.
Using your provided Proxy from text box would not be a problem. However, you should make sure that the proxy is valid and working.
About Me:
I'm a .NET developer with 8 years of professional experience. Please visit my profile to find out more about me. You can also Google my name, "Saeb Amini", to find my website.
I write clean, well-documented code. I communicate regularly during projects and keep my clients updated with their project's progress. Also, I absolutely guarantee your satisfaction or it costs you nothing.
Best,
Saeb
.NET Dev