We did not used a painted/stained combo, but strictly stained. Disclaimer: We did not stain anything ourselves, but paid a finisher to do it before install. We used 'rustic' cherry stained quite dark for all our interior trim, including our wood handrails. Since the entire 1st floor minus office is 'rustic' Maple, Treads and risers are also Maple, stained the same dark color. Balusters are wrought iron. I would say on a scale of 1 to 10 (with 10 being the darkest stain possible before looking black) our cherry trim is probably a 7. Grain pattern is present but not overwhelming, it tends to be tighter on cherry than oak, hickory, or walnut. Our Cherry is not red-hued whatsoever, because its too dark. We had no issue with staining Maple, even though I have heard some on here mention it is impossible to stain Maple dark because it is such a hardwood. A good finisher will know what to do and should have no issues. I say 'rustic' because we requested wood with knots and such, to add more character and we wanted the cherry to match better with our knotty alder interior doors.

Be sure to sell or give away that beautiful old railing and not throw it on a heap. I happen to like it. But indeed, it might look better in black. The railing you have posted instead gave me some shudders. Quite a contrary style and not one I'd welcome in my home. Way too modern for a ranch home, is what comes to my mind. If you are really going to get a new railing, I like the one Judy proposed, although I wouldn't want it in white at your place. Perhaps in black and the railing that matches the wood of the stairs? Or maybe something like this?

The best resource to answer your question is the contractor selected to build the project. They'll be familiar with local codes, alternatives, and costs. By choosing the contractor early in the process and getting them involved during design they can provide value engineering solutions concurrent with design. This streamlines the process, reduces costs and provides better outcomes for the client. To be sure it's a different approach from the traditional deign-bid-build process most architects promote. However, the AIA has endorsed and labeled the process "Integrated Project Delivery."

I understand that OP needs it to be cheap until closing because this is a lender requirement (not unusual) and if it is fixed before closing, it becomes a fixture and stays with the property even if the buyer doesn't close. CONSIDER: A solution to this would be a rehab type loan rather than the typical purchase loan. Benefit to the buyer is they don't need to resort to expensive hard money type loan as mentioned up thread. Also it gives the buyer the TIME to figure out a permanent solution. The buyer can close right away on a rehab loan. The disadvantage to a rehab loan is that the interest rate is slightly higher than your typical purchase mortgage. Something to explore.