I expect my La sportiva's to last about 10 to 12 years or more but they are pricey.
Check out REI outlet
and you can you should be able to find a quality boot for a discounted price. Hint if you get it shipped to a local store you can get free shipping and if you are a member you get a lifetime guarantee even when you buy on sale.
HiTec has cheap boots that are not to bad certainly not a high quality boot but they can be found pretty cheap and will do the job for a couple years.
Quality boots will normally give you more comfort and performance and will last longer than a cheaper boot will and in the long run they should outlast a cheaper pair of boots 2 to one.