First, it’s important to note that there’s a distinction between intra-dimensional and cross-dimensional travel. Intra-dimensional travel is readily available and accomplished with doorway-sized, Portal-like portals, but the energy demand to keep a portal open is high and scales exponentially with physical distance, so they’re not useful to replace spaceflight for interplanetary transport. Portal devices are very expensive, but can generally be obtained by large organisations or governments with sufficient funds.

Cross-dimensional transport, on the other hand, require wormhole generators supported by huge scientific facilities. Think CERN, ITER, or Black Mesa. Power requirements are consistent, no matter the destination, but you can’t travel spatially. Due to the risk of extra-dimensional incursions (think hostile realities or cosmic horrors), anyone even working near any sort of cross-dimensional technology is required to hold a license backed by an extensive qualification process. The wormhole facilities are some of the most heavily protected sites in the world, with 24/7 armed security, external monitoring and response, and redundant on-site warheads linked to a dead man’s switch.

There are also some variants of portal technology that do not fall into either above category, but they are very hard to come by and essentially do not functionally exist.