That's fine in principle, but doesn't always work out in practice.
My first kettle was aluminum. It cost nothing, because I already had it before I started brewing. There was no point in paying out for a kettle that I wouldn't use for another 20 years, and if I did, the quality of the kettles you could get in the mid 1970's is pathetic compared with what you can get nowadays.
My second (enamel) kettle cost me less than $20. It was large enough for full boils, and lasted 7 years. That cost less than $3 per year.
My current kettle cost about $200. I will have to brew until I am 120 for that to be cost effective compared to the enamel.
It's also very difficult to forecast what your requirements are going to be 10 to 20 years into the future (especially if you are just starting out).
-a.