I wonder if allwebhost.com is the best placed to buy a Forex VPS account from? 

I do not have any experience with them but for Forex VPS you can go with budget providers. Cost will be less with similar features.

With any other order: if user makes 6 month prepay - 10% discount; 1 year prepay - 15% discount.
24/7 Dedicated Support, Quick Server Deployment, Scalable Resources. Allwebhost.com forex server hosting is excellent and they also have several ways to get customer support, which is also excellent.

why not?
https://allwebhost.com/forex-vps/
On this page they clearly state that they do offer and support Forex VPS.