Candia - nobody likes losing money, nobody...I have been around BMW's since I was a baby (parents always had one, starting with a '72 Bavaria). I bought an '02 as one of my first cars ('76 Golf 2002) and have had many, many over the years that I buy, work on them a bit (mainly have mechanics work on them to be very honest) but do what I can on my own and keep learning with friends. I am now 52 years old. The car "hobby" is where I have met most of my lifelong friends (BMW aficionados like everyone on this site).
Looking back at all the cars I have "fixed up" to my standards (meaning mainly presentable "drivers," cars focused on suspension and handling first and foremost), I can honestly say I broke even at BEST on ALL of them, with the exception of my 911 Porsche (and that was just dumb luck and timing). Backing out the commision etc. I still didn't "kill it" on the sale.
Point being was what I mentioned above, for most of us this should be looked at as a "hobby." Your business is in construction. Make your money there, win some, lose some on the cars, look at it as a "hobby." Learn and enjoy the experiences you have along the way (good and bad) and keep enjoying the hobby. Don't let one car get to you.
You are at the point where you realize you are in over your head and basically would be throwing good money after bad. My advice is take whatever the high bid is, you can lower your reserve at anytime, speak with BaT and let this bird fly away. Widdle down the collection to one car (very smart) and go nuts on that one and I think you will have a much better time in the "hobby" we all truly enjoy (most of the time...LOL).
Good luck, clock is ticking, time to make some hard decisions. If this goes RNM, good luck finding a private buyer that would pay more or another site where you would get more for it. As you know, listing on BaT is a lot of work, why throw all that away too? And my 2 cents, the market is softening again unless it is a highly desirable car, rare, low production, etc. But hot rodded coupe, I think you won't find a better place to sell than BaT at the moment.