Although renting points is technically not allowed by
DVC - as you can see, it is very popular.
The way it works is you have a DVC owner make a reservation in your name for the resort and dates you want to go and you then work out a payment to compensate the owner for the use of the points that pay for the reservation.
As far as price is concerned, you can save, in my best guess anywhere from 25% to 75% over what an equivalent cash, hotel reservation would cost.
The differences between the prices are dependent upon the dates (season) / resort / type of accommodations, etc.
Some times the accommodation are exactly the same, sometimes they are close but not exactly the same.
I had 8 days in a 2 BR Concierge , Jambo house reservation for this past holiday season that cost about about 500 points - typical prices for those points would be between $10.00 and $12.00 pp translating into $5-6$K for a stay that, if booked direct through Disney - would have been $24,000.
This is at the extreme end of the savings - I would think that the majority of persons renting points garner about a 50% savings.
There are commercial renters and private ones, anyone who is doing this properly will use a contract to protect both parties.
I just rented someone a 157 point stay for 2 adults, 2 kids. 9 days in August in a Savannah view studio @ $10.00 pp = $1570.00 .
According to the site today, the equivalent in beds ( 2 queens in a Savannah view ) is $3381.00.
Take a look at the rent trade boards overview links - there is plenty of great info there for new renters.
Hope this helps!