I've been thinking about root server hosters recently and a friend pointed me towards Digital Ocean. And besides their good pricing and choice in OSes I really like that you can pay by the hour. That means you can use a server for a few hours, shut it down again, create a snapshot, and "detroy" it. You keep the state of your machine and you can return to this state easily at any time.
A server with 512 MB RAM, 20 GB SSD and 1 TB transfer costs you 5 $ per month. But you can also use a server just for an hour for just one cent or precisely $ 0.007. This is very cheap yet comfortable for remotely testing things. And you get a fully set up Ubuntu or other server in just under a minute. Just remember to shut it down, snapshot and destory the server when you're finished if you want to pause the billing. And they have servers in Amsterdam / EU.
Of course, you could also use this to create your own private cloud service. Try it out!
Note: I get a provision for referrals if you click the link. But I wrote about it because I like it, not for the money. I may have written more than I would have otherwise, though. ;)