Jokerman the body type you are refering to is ectomorph, it's true that if you are born with this body type then you'll never be a profeessional bodybuilder or anything like that but you can drastically alter you muscle mass and become what most people would term as "stacked".
I've been training for two years and i've put on 11kg in that time and I was skinny as hell, a famous example of some one going from very skinny to very large is luis ferrigno (granted he took steroids)
You are right that most weight gainers do not work and are exspensive, but if you did want to take something to increase the muscle gains, creatine is the strongest non harmfull supplement out there, it has been clinacally proven to help 70% who take it to help them gain 14 pounds within three weeks (didn't work for me though

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But I say agian, DIET IS THE SINGLE MOST IMPORTANT THING THAT WILL HELP YOU GET TO THE SIZE THAT YOU WANT!! SO GET THAT SORTED