I think I read somewhere in another thread that while WK does not have PayPal as a standard option on the payment screen, they do accept PayPal.
If I remember correctly, you would need to contact staff by email, whereupon they provided you with a sort of ‘PayPal invoice’.
In any case, the staff is really friendly, so even if you just want to check out your options and aren’t sure whether you want to purchase, I wouldn’t hesitate to contact them! 
Edit: here’s a thread by someone who managed to subscribe by PayPal as evidenced by their 3> level. 