Forget the advice from "some guy at the store." Wood conditioners are meant to prevent splotching, but they do a poor job at that. Stains are of two basic types - Pigments : finely ground powders - Dyes : chemicals that are dissolved Think of third grade science where you put dirt in a jar of water and shook it and sugar in a jar of water and shook it. What was the difference the next day? The dirt mostly settled out to the bottom. The sugar remained in solution. Pigments work like the dirt and dye like the sugar. The big contrast comes about because the earlywood (large pores) get a lot of pigment in them and the latewood (hard and smooth), does not absorb so much because it's wiped off. Dyes, on the other hand will absorb more evenly and reduce the contrast (at least color wise). So, what you want is a dye. Problem is, Minwax stains are sometimes dyes, sometimes pigments, and often both. They don't tell you. I suggest looking up Bob Flexner's "Understanding Wood Finishing" at your local library, where he shows photos of oak dyed on one half and pigmented on the other. Then get some scrap of oak and test out your intended products and processes on the scrap before starting on your newel post. It's easier to not make a mistake than it is to recover from one. You can get dyes at most woodworking stores such as Rockler and Woodcraft, or via mail order. You can control the concentration by how much dye you add to solvent (distilled water in most cases). So you might want to mix up a series of concentrations and apply each to see the resulting color. But to see the true color, you will have to apply the finish coats as finishes intensify the stain colors.

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.

This needs a rail on the close side or it is a safety hazard, and the hand rail needs to be able to go continuously from top to bottom, so it would be helpful to see up the stairs. What style are you going for? Would a classic wood railing in trim color not work? You could go black metal if you wanted something a bit more unique, but you'd need other black metal accents to compliment it.

Curious, inside or outside? If inside, what does it matter how cold it is? And my 11 yo is studying geography. The mid-west has an enormous variation in average winter temp. The difference between Minneapolis and Chicago is bigger than the difference between New York and Atlanta.