Who purchases the husbands wedding band?

In my case? The husband.

tutuzdad-ga

In our case, my husband bought my wedding band and I bought his (they
are matching plain, wide gold bands. I do not have a big fancy diamond
engagement ring - never wanted one, still don't). We were in the store
at the same time, but wrote separate checks. We were living together
at the time and pretty much sharing finances, but it seemed fitting to
at least make the symbolic gesture of buying each other's ring.

Modern etiquette usually prefers that what is openly accepted by the
parties involved can seldom be wrong, if no laws are broken and no one
is harmed.

If it is not accepted equally  by the parties involved, and is causing
serious friction, those about to be married probably should seek
pre-marital counseling before it is too late. Seriously.

There is no law that I know of that either bride or groom even have a
wedding ring, though there could be local laws that I would not be
aware of. This is tradition, and probably a descendant of pagan
tradition, and no more.  In my experience, such issues usually (but
not always) result from outsiders -- who certainly can cause a lot of
grief when they try to force their views on the marital couple.

If a man asked me that question, I'd probably tell him, "Who cares? 
If there is a problem, go to a mall jewelry store and buy yourself
what you can afford and doesn't hurt your finger. And, if the
bride-to-be makes a scene, walk away from this wedding, it gets worse
after you are married, and if a stupid wedding ring can cause this
much fuss, your marriage days are numbered before they start."

And, If a woman asked the same question, my answer wouldn't change
much, except I'd recommend she not try to force her future groom to do
something he doesn't want, just to impress her friends.

By the way, I worked as an electronic technician on high voltage
equipment, and it was insane to wear a ring. So, I didn't wear one,
and chose not to buy one at all. And, I guarantee you, the lack of a
ring did not interfere with my fidelity to my wife of 30+ years.