Let's Talk Deposits Con Cars

My wife has been without a car for a while. She's got very eccclectic tastes and has had her heart set on a manual Honda Civic hatchback. Unfortunately, the newer models (2002+) have power steering but the older ones do not. Anyway... Her "requirements" are a bit specific

Yesterday, she found the car she wants. We ran Carfax on it and it's checking out. Not only is the car exactly as she wants but it's purple - her favorite color. So... this is like her ultimate "thing".

But we can't afford it right now. That is to say, we paid off credit cards in September and have only saved a few grand since then. WE can certainly afford the car, just that we didn't plan on buying it today and didn't "conserve" our paychecks this week. I plan to drive up there today and put a deposit on the car until we get paid again but...

How long is "reasonable" to keep a deposit on a car before actually making the purchase? When I bought my last one, I put the deposit down and then decided to buy about 8 hours later so I've never "tested the waters" there. In this case, we will have the money by next payday (January 17th) - is that reasonable or too long?

I'd say the only opinion that matters is the person who is selling the car.
Best of luck hope swmbo gets what she wants.