First step is to kill a bear.I know that is a no brainer but the size and quality of the bear will have influence on what option would display it best and how much you want to invest in it.
Know that all taxidermy work isn't created equal.My advice would be find a quality taxidermist with a good reputation,now,and get some suggestions from him.He may be able to show you photos of options or possibly finished work.
You should get the skull cleaned regardless of what else you decide.
Just tanning the hide would be one of the cheapest options.
A rug has the hide tanned,head mounted and usually a decorative,double felt border around the edge plus is lined on the bottom and should be padded.They are a lot of work and take up a big chunk of floor or wall space.
A shoulder mount will cost a few hundred-closed mouth is cheaper.They don't take up much space.
Another version of the shoulder mount is a pedestal mount.This is a shoulder mount attached to a habitat base and sits on a table,shelf,etc.They cost more than a shoulder but there is no end to the creative possibilities depending on the taxidermist.These can have a lot of eye appeal.
A half lifesize doesn't take up a lot of space but normally costs 75% of the price of a full lifesize.It can be creative too or just a half bear coming out of the wall.
A full mount is a big investment and you probably should reserve this option for a really good quality bear.Quality to you may be a huge bear,a great quality skin,a different color or all of the above.There are a few options as far as poses and the taxidermist can help you choose one that best shows the positive attribute of your bear.
Keep in mind,the best hair on the bear is on his sides and back.The weakest is on his belly.Sometimes a bear on hind legs exhibits more of the weak belly hair and less of the thick body hair.It doesn't always show the best part of the bear.
Your taxidermist can give you a range of prices for the different options but don't get to set on anything until you get your bear.
It's kind of like trying to set up a properly tuned batch of arrows but you haven't bought the bow yet.