I have significant experience in low-level Windows development, including driver development (kernel mode), cracking and reverse engineering. I use the most advanced tools of the trade including IDA Pro, OllyDbg, WinDbg and other Windows SDK/WDK tools, Windows SysInternals utilities, and others as needed.
If you are looking to simply decompile a single exe file into C source code I can do that for you for 500 USD. However, it needs to be said that the produced code, though accurate, will not be very readable as a compiled program does not retain identifier names (like variable and function names) that usually convey most of the meaning in source code; still, the code's logic is usually fully and correctly retained.
Also, the code won't be much more than a long monolithic list of statements that is usually not directly compilable into the same application whose decompilation produced it.
Therefore, in most cases, such projects involve a specific function (or set of functions) that need to be decompiled AND converted to meaningful source code that can then be compiled into a new and fully working application. The process of doing the latter usually involves debugging the app to see which function/functions are being called and when and then extracting the decompiled code of those particular functions, rewriting it, in order to become comprehensible, and then combining it with other code into a new project structure (could be a Visual Studio project) that can then be compiled into a new fully working app.
If what you want is what I described in the last paragraph then I can do that as well and the cost for each function/functionality depends on the function/functionality itself and its complexity. Specific quotation for this scenario will be possible after a first full decompilation of the app is performed.