It depends on your utilisation vs. idle time. EC2 is more expensive than most other virtual server providers, but they let you start up or shut down many server

It depends on your utilisation vs. idle time. EC2 is more expensive than most other virtual server providers, but they let you start up or shut down many servers within minutes, and bill hourly instead of monthly. If your load requirements are mostly fixed and spread out evenly, alternatives including buying your own hardware may be cheaper. If you do a lot of number crunching in short (hours or days) bursts, EC2 can be significantly cheaper, as you are not paying for the idle time. Of course, if the numerical computation is scalable across computers, it can be made bursty - instead of running one average server for a month, you could use 30 servers for a day and get the results faster for the same total cost.