Bike Friday?? They're folding bikes - low main tube and can be custom sized. They fold, so you can generally bag them and take them on transit at any time (in my experience). They can be set up as road, commuter, touring, mountain and anything in between.
We had a few issues with ours when we got them, but we've worked them out, and I would recommend them. They have a wide range of prices (I don't think any are in the really low cost category), but you might be able to find something pre-owned through the company or on ebay.
Just a thought
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