The minimum first-time purchase through Disney is 150 points so you can't buy a 50 point contract direct from Disney.
Resale, you can purchase any contract you want. The 150 point minimum does not apply. A 50 point contract of course would mean that it is not an initial contract but an add-on for someone else. Example: Someone bought 150 points at BWV, then added a 50 point add-on at BCV, and now has decided to sell the 50 point contract.
You can purchase the 50 point contract from a seller as your initial purchase. The 150 point minimum does not apply to direct private sales.
Closing costs generally run in the $400-$450 range for most contracts, say in the 50 to 400 point ranges. After that the closing costs tend to go up on larger and larger contracts. So at $400 that's adding $8/point to the purchase price. Thus if you find a 50 point resale for $70, you're going to pay $78 by the time you add in the closing costs.
For resale contracts you will need to find your own financing, either cash or a loan. A home equity loan works well for most people.
The value of a resale can vary a lot by how points have been used already. For example if a 50 point contract can be found that has all 50 of the previous year's points already banked, that's a bonus. If on the other hand a contract is found that already has all the following year's points borrowed and used already, then that's a negative point and that contract has less value.
All contracts are negotiable between buyer and seller just like any other real estate transaction.
Hope this helps. Good Luck