I don't mind the sales tax since it isn't taxing the merchant. It's taxing the consumers. At the moment there is 0% tax on the consumers. You just pay whatever is listed.

However, if you include both taxes, it totals up to 10% or less, which is the same as bazaar tax on players selling. Although, player bazaar tax doesn't have a upper cap limit, so purchasing from MW still saves more gil.

If 4000gil or less is breaking your budget, then you still have the option of going down and picking up the item. Keyword there is option.