Just how much is an okonomiyaki cart?

[Anchoku]

Try at least $8000 like this low-quality ramen stand.

[A.Nonymous]

That even looks like Ukyo's cart...although maybe a bit smaller. Take into account that Ukyo's cart also looked seriously used and I'd say it's about a wash.
I remember, years ago, our local weatherman (Fritz Colmen) in Los Angeles went on a trip to Japan. One of the things he talked about was the ramen carts. He said that a high quality one, all shiny steel, could go for about $37,000...it has been years, so I might be mis-remembering the number.
I've got a question about Ukyo's secret sauce, she made a big deal about tasting it 10 years later...shouldn't it have been in the cart when Genma ran off with it?

[Anchoku]

I've got a question about Ukyo's secret sauce, she made a big deal about tasting it 10 years later...shouldn't it have been in the cart when Genma ran off with it?

A lot of traditional pickling was (and still is) done in the ground. The cool earth stays fairly constant in temperature whereas a storage shed would go up and down a lot in temperature over the seasons. (Look up "thousand year old eggs" in China.) I think kimchi is also pickled and buried.
Maybe it's a difference in background but it made sense to me when Ukyou buried her jar in the earth. Over time, the flavors from each ingredient would blend without having to boil them together, which changes the flavor. Two examples you may be more familiar with are sun-tea and pickled cucumbers. Letting the tea steep in cool water for a long time gives tea a slightly different flavor than hot tea because boiling water rips a lot of chemicals from the leaves, quickly. (Cucumber) pickle commercials used to claim how "crisp", "crunchy" and "fresh" they were because they weren't boiled in the canning process. However, pickling vegetables at low temperatures takes longer. Hence the reason for burying kimchi. Boiled cabbage gets mushy.
Overall, long, slow, traditional methods of making food carry the implication the result should be of the highest quality; not taste like dirt, twigs and grass. There's the dichotomy Takahashi-san was presenting. Despite how burying food in a pot for 10 years appears to modern culture, Ukyou's secret sauce was supposed to be her culinary master-work; like a thesis for a masters degree. For Ukyou to let Ranma eat all of it shows mind-boggling dedication to her fiance.