Mentioning set make me believe that you are talking GPU mining, not ASIC mining, so I will talk about GPU.
How much it will cost?
A full rig can cost $1000 or can cost $10,000 it all depends on your budget and what you want to mine.
How long you can mine with your GPUs?
It depends on how you treat your cards, cards that have been treated well and maintained well will for sure have a longer lifespan than others. There is a lot of guides on how to maintain your cards. Also, all the cards should have lifespan running hours in there manual but in most cases, it is not accurate. I have come to learn that maintain your GPU fans alone should give you a good boost in there lifetime.
Before start with anything you should make some research to get an idea of what will be getting yourself into, there is a lot of websites that will help you a lot in choosing the best ROI card and the best coin to mine, you can start by check this website. (whattomine)