https://www.vcarious.com/how-are-effective-electric-dog-fences-for-dogs-large-in-size/ vcarious.com
You cannot generalize the fact as only expensive electric dog fences are the best. But you need to understand facts that why most of the electric fences are quite expensive-
The most important element in the electric fence is the wire, and you cannot use a thinner wire as it will be unable to work from the underground placement. Moreover, the accuracy will not be very effective. Some experts mention using copper wire to ensure the best results. So, these changes make the piece expensive to some extent.
If your area is large and looking to boundary the whole area for the dog to be free and play on its own, you need more length of wire and a good quality transmitter. The larger the area, the more powerful the transmitter you require. It also adds to the budget for the electric fence.
The packaged electric fences provide only a limited amount of wire. If your area is larger and you need more wire, that is your extra expense. If you can contact the manufacturers and order a customized piece, you will get the required length of wire, unlike the cheap electric fence for dogs.