Buying hydrangea plants or shrubs can be expensive. If I need a special perennial for the yard I try to wait until the end of the growing season to buy them on sale, but even then they can cost a lot.
If you have the patience to start a hydrangea from one already established in your yard, you can save a bunch of money and within a year or two that plant will be the size of the ones for sale in local nurseries.
Maybe a neighbor or relative who already has established plants would offer to let you start one from theirs. I find that cuttings are a bit more difficult to do, so take many. Or go into their yard with them and look for hanging branches that are already rooted.