Fair question. If everyone thinks they need to have a $18K bike then the sport would be very limited outside of sponsored athletes. That is not what you are going to see at races though.

My first triathlon was done with 5-6 of my friends. I didn't have a race bike or access to a pool, so I decided to just follow my favorite half marathon training plan and not try to train for the bike or swim legs at all. I borrowed a race bike from a friend of my brother for the race and went and had fun. I did something like 3:30 min/100 swim time, averaged around 21.5 MPH on the bike, and had the 2nd fastest run split of the day for about an 8th place out of about 15 people in my AG finish. That is how people get into this sport. They compete with what they have and don't try to compete with people on $18K bikes.

My first Tri bike was $300, my second Tri bike was $1,500, and my current tribike was $1,600 with aero carbon race wheels and it only had 2,000 miles on in.

You don't have to break the bank to be a triathlete. I averaged 24.2 MPH average for the bike leg at my last race on the $1,600 bike. When I had the $300 bike I used to love coasting past people on $10K bike when going down long hills in races.

Let's be clear. The paid advertising is designed to make it look like everyone who is serious about the sport has an $18K bike, but that is defiantly not true. I followed a local athlete when I started the sport who's resume included a 2nd place over all finish as USAT Duathlon Nationals and a 1st place over all AG finish at Ironman Texas. He did all that without funds for aero carbon race wheels and competing on a low budget bike. If you talk to people at races you will find that no one is racing on an $18K bike. I am guessing that you will find that most of the serious triathletes are on bike that are under $2,500 and that entry level athletes are completing on mountain bikes that they had before they got into the sport or entry level street bike. Paid advertisement is not aimed at grow the sport. It is aimed at making sales to people already in the sport.

Don't get me wrong there are lots of sports that are cheaper than Triathlons. Especially at the pointy end, but we should not be driving the false narrative that you need an $18K TT bike to get into the sport. Anything that you have kicking around the garage rusting out will do the trick. Especially if you are doing it to change up your cross fit routine and not with the goal to complete for podiums.