Currently reported/confirmed (discord)
The Second/Hill Shop costs 100g to view what you want to do with it
it has a single set of choices that can be chosen from a multiple set of choices
The resulting cost from the single set of choices claims that it costs 90g to do everything stated.
A charge of 810g will then be made - if you have anything less than that, it will zero you out, anything more, it'll still charge 810... (obviously...)
The only real thing a client can do atm to combat this is to buy it with very little above 100g, or to spend enough of the extra on ingots and parts, as long as you have 100g, you'll be able to make the transaction.