The Mages Guild operates a teleportation service at reasonable rates (and really cheap if you are a guild member). Travel is instantaneous in both real-time and game-time. The only drawback is that it only works between the five Mages Guildhalls (Ald'ruhn, Balmora, Caldera, Sadrith Mora, and Vivec).
Pricing does not seem to be reciprocal. For example, it might cost 7 gold to travel between Vivec and Sadrith Mora, but only 5 gold pieces to travel from Sadrith Mora to Vivec. They must have hired an airline pricing consultant ("If you purchase you tickets five years in advance and travel on a Tuesday while wearing a pink tutu and argyle knee socks and stay over the Feast of St. Mathias...").