You can get pretty sleek mini-pc in the price but, there performance is sub-par compared to the price they are asking for.
While itx for factor is very expensive, m-atx is cheaper and there are quite few sleek cases for them.
If you are looking for prebuilt mini pc, asustor flashtor is pretty sleek if you only want m.2 storage.
If going for an inverter try a sin wave one if it’s in your budget.