I posted this previously in another thread, but am reposting it here. I've been using this rack for several months with no issues on my RadMini Step Thru:
It fit almost perfectly and allowed me to attach a large Raleigh rear basket. I doubt it's as strong as RAD's rack, but it holds a ton of stuff and the rack itself is super light. I've attached a photo of it on my bike. You can find them cheaper from different sellers. I just posted the link above for the photo reference. I got mine for about half that price from a different seller in the spring, but that listing is no longer available.