ICON provides a couple of test environments, where you can deploy and test your SCORE without ICX. Below is the information about the networks that ICON foundation operates. When you send a transaction, make sure you use the correct network id (nid) in your transaction. If the network id does not match, the transaction will fail.
Alternatively, you may want to have own private blockchain network for your development, or even for your commercial service. Below guidelines explain how to set up a private network with the same source code that the ICON mainnet is using.