Is it possible to use bitcoin-core's RPC api (assuming the full blockchain is downloaded locally) to type in any public bitcoin address/key and get back the amount of bitcoin associated with that address/key?  I am wanting to learn more by trying to create a website similar to blockchain.info where people can simply type in a bitcoin address/key and see how much bitcoin is associated with that address/key.

I have tried using some of the existing 3rd party API's but those are either too close or expensive or both, so was thinking about creating something myself locally.