Reverse a Embedded C executable

We have an Embedded program (We believe written in MS Visual C) that we need code extracted. The developer is out of business and not accessible. It does communications with another device via a RS232/485 port and was done about 20 years ago. We shall pay for some hours to review the executable for you to come up with a fixed price to decompile to some point that it can be upgraded to current version of C in editable form. Please share your willingness, capability to do this work. Only short listed candidates will be provided with the exe. All the extracted C code will be given to us and will be tested later by us and we may need some help from you during implementation as well. We do not have a budget set aside and are looking for the best deal we can get with delivered acceptable solution.