There is a feat called Create Portal from the Forgotten Realms Campaign Setting (pg. 34).
You have learned the ancient craft of creating a portal, a permanent magic device that that instantaneously transports those who know its secrets from one locale to another. Faerun is riddled with portals.
Prerequisite: Craft Wondrous Item (PH)
Benefit: You can create any portal whose prerequisites you meet.
Crafting a portal takes one day for each 1,000 gp in its base price. To craft a portal, you must spend 1/25 of its base price in XP and use up raw materials costing half of this base price. See Chapter 2: Magic for details of portal creation. Some portals incur extra costs in material components or XP as noted in their descriptions. These costs are in addition to those derived from the portals base price.
From Chapter 2: Magic (pg. 61):
Base Cost: The builder must spend 50,000 gp on raw materials to create a single, continuously active one-way portal [...] The builder can create a second portal at the destination point, making a two-way portal for half price (25,000 gp, fifty days, 2,000 XP).
So in total this would craft a two-way portal for 75,000 gp and 6,000 XP, which is cheaper than your wondrous item, depending on how you valuate XP. There are also plenty of rules for restricting access, creating larger or smaller portals, and anything else in that section of the Forgotten Realms Campaign Setting.
Note that in order for a portal to be crafted between planes, the creator must know the gate spell.
As far as your further specifications (pg. 59):
Unless the builder has preset some limit, any number of creatures can pass through a portal each round. A creature using a portal can take along up to 850 pounds of gear. In this case, gear is anything a creature carries or touches.