>>1078317Simple:
Scan for good used bike deals.
Ask a lot of details from the seller.
Check stolen bike records with the frame number.
If anything seems too off, just walk away.
Definitely go for as modern as possible. (It will ride faster and feel better. Looks more sleek too.)
Remember, if you look after your bike, it will hold at least 5-10 years.
I got my Trek1.2 2008 (~9,6kg) for about 200$. Best deal ever.
TL;DR the best bang for the buck is second hand modern.