That's not an investment. The consensus around here seems to be that SIC time is pretty worthless as it is. You have a good amout of total time, getting the PIC time is probably more important in your case. Flying night freight you should also know that there are a number of companies out there that you would be able to go to for a couple years, upgrade to captain of something like a falcon 20 fast and get a lot of PIC time while being paid for it rather than paying them.

Take some pride in yourself, in your profession, and in your fellow pilots. Help them, and help yourself by being compensated for your services. Remember, even prostitutes get paid for their services.