Houses cost a variety of different prices, the price varies on the amount of storage boxes you can put in them.
Once you own a house you can spawn their if you wish,
But you will not be able to store anything in it unless you head to the market to buy a storage box, their is 2 types of storage box large and small.
to put the storage boxes in your house, stand in the house press "Y" click on the storage box and click "USE" it will place the box in your house in a predefined location.
you can then store items in your house it is very simple to a vehicle you have a trunk inventory to store weapons plus you have a "T" inventory to store your trusty weed and spike strips
A point to note once you place your storage box's they can not be removed, when you sell the house you do lose your boxes so purchase carefully they are not cheap