Hi,
Since you have asked:
Registration fee (to put it in your name)
Somewhere to keep it.
That's it.
If you want to fly it then somewhere to keep it becomes more complex:
ie hangerage to keep it at an airfield, a bottle of whisky to a farmer to use his field or trailer it to and from your home.
You'll also need a licence and third party insurance - about 150 quid - to fly it.
Maintenance and annual permit are all variable, as are running costs (ie fuel and oil)
Getting a licence is another lengthy topic too, and much of what is said on Pprune regarding overseas light aircraft training applies to microlights too - except that the only microlight training recognised by the UK CAA is that carried out by UK microlight instructors.
Have a few lessons first, chat to fellow club members - and, dare I say it, your instructor.
Or feel free to give me a phone on a rainy day - 0797 997 1301
Very best,
XA