In most cases, the warranty isn't worth the paper it's printed on. All of the ones I looked at covered parts only so you'd have to pay the labor costs for diagnosis and installation of the covered part. I too started by getting quotes from HVAC companies. I was quoted over $5500 to install an 18K BTU Daikin mini split in my garage.
I ended up getting my EPA 608 Universal certification, ordering a Senville Leto 24K BTU from Senville for $1200. Tools (Micron gauge, vacuum pump, valve core removal tools, tubing bender, flaring tool, etc.) cost me approx $500, supplies (equipment pad, service disconnect, service whip, breaker, Romex) added another $250 or so, and electrical and mechanical permits were $110 total. All in, the system cost was bit over $2K.
I submitted the warranty registration paperwork to Senville and included my EPA certification number in the HVAC Contractor License Number field and received a confirmation that the warranty was successfully registered. I assume this means I'm good to go if I need to file a warranty claim. If so, great. If not, not a huge loss. I've saved enough money installing it myself that I can actually buy two+ new systems before I exceed the cost of a "pro" install.