It's quite feasible to add a loader to most tractors. Whether that is ideal or not is another question.
If buying used in that range, I wouldn't consider putting a FEL on one that doesn't have power steering and front wheel assist as that loader will just be too much weight. Steering would be very difficult and when fully loaded, the FEL will push the front tires down in soft soil making it hard for the rears to push it up and out of the indention without front wheels assisting.
If you can find a used tractor with a FEL, you'll probably do better price-wise than buying a new FEL later. After market loaders will cost in the range of $2K to $4K depending on the loader. From what I've seen, a used loader doesn't usually add more than about $1500 at most to a used tractor.
As long as the used loader has good integrity (no bad welds, no cracks in key components, etc.) the value of it with a used tractor is good.
John