a1.large is an AWS EC2 instance with 2 vCPUs, 4 GiB memory (AWS Graviton Processor). In US East (N. Virginia) it costs $0.051 per hour on demand ($37.23 per month) for Linux; a 1-year reserved instance with no upfront costs $0.0321 per hour, 37% less. Spot capacity is about $0.0477 per hour. It is sold in 9 regions; the cheapest is Asia Pacific (Mumbai) at $0.051 per hour.
Prices by region
USD per hour, Linux. Reserved prices are no upfront, standard. Cheapest on-demand first.