Spot instances are cheap because you're buying leftover capacity from AWS, but they can turn your server off at any time. Probably not a good choice for algotrading where you want to be online 24/7. You'd have to use on-demand then. I use AWS for work and looked into it, but decided not to do it in the end because they are so expensive. For businesses that might be worth it because they also have a ton of enterprise features built in, but you won't need those as a single individual. I have a VPS with OVHcloud, but I've heard good things about digital ocean too.