Charity rides are a great place to start if you have an interest in cycling.
They really take good care of the riders at most charity events.
First, find out what the course is like.
If it is flat, just about any bike will do.
If it is rolling or hilly, you want to get a touring bike.
That way, you will have extra low gears for climbing hills.
Also, the frame geometry on a touring bike is better suited to long rides than a racing bike.
Either way, it is well worth it to buy your bike at a good bike shop.
If you want to hang the bike in the garage, buy it at a discount store.
If you want to ride it, buy it at a bike shop.
Used bikes at a club sponsored bike swap can be good also.
Train.
For an 80 mile ride, you want to work up to the point where you ride around 150 to 200 miles per week.
2 weeks before the event, ride at least 60 miles in one day.
The training guides say to not increase your weekly miles by more than 10% at a time.
While you want to gradually increase your miles, it is MOST important to limit how much longer your longest ride per week is.
If on your first week of training, you do 20 total miles and 1 10 mile ride, you can safely increase the long ride to 12 miles while doubling your total miles by riding 8 miles or less on the other days.
If you want to see what is the extreme in distance cycling, check out the Race Across America. Otherwise known as R.A.A.M.
The R.A.A.M. race runs from San Diego to Atlantic City.
The winner in the individual class takes just over 8 days to peddle the entire distance.
If you decide to take up the charity ride and want any other advice or insights, just let me know.
Chas
