Keeping costs down in UTV racing is simple; forget building the stock engines & 4wd systems, and stick with a simple, 2wd, no reverse system, with a stock streetbike engine.
Ridiculously cheaper to start with.
Light years more reliable.
Engines/transmissions live MUCH longer.
MUCH cheaper to maintain.
MUCH cheaper to repair or replace engines/transmissions.
Anyone with basic wrenching skills can build & maintain one.
The above listed is the key to keeping racing going, and gaining new competitors. They're also:
Faster.
Make more power.
More versatile.
A 1000cc streetbike powered UTV can race short course (with lap times on par with 150k Pro-Lites), race desert, and can climb any hill at Glamis, even on short course tires. Where else can you race in a professional series, yet take the same car out for recreation use? It's practically unheard of.
One could write a healthy list showing the pros of using streetbike engines, and the cons of using a UTV engine. What I've listed is just the tip of the iceberg.