Sir,
The 34-1 was first produced in 1960, according to the SCSW(Standard Catalog of Smith and Wesson). With an engineering change in 1988 it became the 34-2. The model was discontinued in 1991.
I believe that the M18 is generally considered more valuable than the M34. The evidence for this is that there are far fewer for sale than there are 34s(at least the last time I looked). Also, if you follow the forum discussions here, you'll find almost no one who regards their 18 with anything less than glowing accolades.
My 18, for instance, is the only one of my Smiths that has absolutely no noticeable flaws. Everything about it demonstrates excellence. I've no intention of ever selliing it.
My guess is that the person who sold you your 18 at such a low price hasn't kept up with the going rate for them. That or he is just a very generous person.
Regards,
Andy