What version did your have? - it it was iPhoto '11 then you can do a free update to iPhoto '11 version 9.5.x in the App store - if it was an older version then you must purchase (and NO it is not a LOT of money - it is $15.00 - not a lot at all) an upgrade to iPhoto '11 version 9.5.x - upgrades are not and never have been free
If you previously owned iPhoto '11, sign into the AppStore with the AppleID you used to buy iPhoto and look at the Purchased Tab. You may find iPhoto waiting there ready for download.
If iPhoto came not preinstalled on a Mac with LIon or later, but with an earlier system, look for your system installation media. The bundled application CD, that came with MacOS X 10.6.x will probably contain an iPhoto installer.
But if your previuos version was not iPhoto '11, you'll have to buy the new iPhoto version, to be compatible with Mavericks.