So what i think you're saying is you want a device that will teleport you somewhere when you put a certain item in a hopper.
I would connect the hopper to a sorting system so it only works if you put in the right item. Then i would make it take a comparator output from a hopper when it detects the correct item so it powers the command block to teleport you wherever you want. This is how i would do it:
You will need to build an item sorter, which looks like this: (Note, the chest at the top right is where everything except the correct item will go. eg if you want only a diamond to activate the command, everything that is not a diamond will go into that chest.)
The hopper directly to the right of the comparator in the sorting system (see the above picture) must be filled with the item that will active the command like so (you can obviously replace diamonds with whatever item you had in mind).
After you fill the correct hopper with your item (above picture) make hoppers going down from it and connect it up to this system:
The command block will contain the teleport command (eg. ./tp @p 357 70 2470)
The chest will contain all the diamonds after they have activated the command block.
Build all this correctly. and it will only activate the command block when a diamond is put into the hopper, and all the items put in will be stored in chests.