The price in the US excludes sales tax (normally around 7-10% depending on the state). The UK price includes 20% VAT. Take the tax off the UK price and the prices are very similar at today's exchange rate.
You can set this as a workout and schedule it in your calendar then upload it to your watch which as you can tell, it's a really manual process... It is possible though! Sorry this answer came very late, you probably made up your mind on this watch already.
No, it is not posssible to store music on the watch. It does have a control screen which lets you control music played on a paired phone. Which means you have to take your phone with you. Fitbit and Apple watches have the ability to play music without a phone.