Since bras are so expensive, is it appropriate to wear them outside the T-shirt or show the bra with see through dresses?

Although I do understand your question, I sincerely question your logic.

A lot of things are expensive, but that doesn’t mean we should wear them outside our shirts.

Lingerie is expensive. Should we wear lingerie on top of our day clothes?

So let’s start by uncoupling these two things. Being expensive has no relationship whatsoever to what we wear in public. I have an expensive pair of panties — should I wear them outside my jeans? Of course not.

As far as the other part of your question, is it okay to wear a bra with a see-through dress? Yes, this is done all the time.

Here’s a photo of Nicole Richie. We can easily see her bra, and she’s probably proud of wearing it too. Look at how self-confident she looks in this photo.

Here’s a stunning photo of Rihanna wearing a white mesh outfit with a visible white bra showing underneath. These are all fashionable looks, and all three of these pics show nicer quality bras which makes perfect sense if they are visible to the general public. You can easily see that none of them are worn outside the shirts.