A few people have been scammed on the site, Only use paypal to pay for items for sale by other members. If they will not use paypal, its likely a scam NEVER SEND E-TRANSFERS OF ANY KIND.
This gadget will hold it in place. I got it to hold cell phone but it should work with transponder too. Link is here Amazon.com: Bike & Motorcycle Cell Phone Mount - For iPhone 6 (5, 6s Plus), Samsung Galaxy Note or any Smartphone & GPS - Universal Mountain & Road Bicycle Handlebar Cradle...