Try a GPL club like GPLDL. They have free items.
Try Divi and inside it will let you download pre-designed pages. It has 128 layout packs but they are very basic
You can also try another GPL club called GPL.Coffee. They charge for memberships
They have many more powerful ones than Divi
iEvent
Eventum
Event Station
Event Champ
Event Talk
VentCamp
These are full blown Event systems. You should buy it if it is a legit event. You cannot afford any problems when working on a project involving many thousands of dollars.
Whatever one you choose, if it is a big event, use EventBrite for ticketing and make sure your website ticketing plugin hooks into it. GPLDL has the Modern Tribe Events Plugins and one of them interfaces with EventBrite so you can make a test site, hook it up and see how it works.
Events are a big can of worms, making sure the workflow from web search -> sell them on the event -> buy ticket -> get them in the door -> scan the bracelet to see if they can enter a certain training session, etc, etc. Lots of integration.
Advice - Put the system together and TEST IT EVERY DAY FOR TWO WEEKS to make sure it works. Get as many people as possible trying to break it. Only then can you trust it on event day.
Also if it is a big event where you are paying the planner$10K - $20K - $50K, make sure they ALREADY have this in place. If they cannot explain EVERY DETAIL, then get a new planner. They are not your friend and they are not doing you a favor. And get 4 or 5 quotes from different planners and find out what they offer. It is like buying a house, always get everything in writing.
Sincerely,
TheEye