If I want my limousine customers to start signing liability waivers as I cannot afford commercial insurance, what are the risks and can a liability waiver hold up in court if I’m ever sued?

If I were you, I would never rely on the answer of an internet lawyer to this question.  It involves many complicated issues.

In Florida, the owner of a vehicle is responsible for injuries caused by the vehicle and cannot waive that responsibility.  You could title the vehicles in the your company name, but the company's assets would be at risk for injuries.  I do not know how Utah treats this issue because state laws vary widely about this kind of responsibility.

In Florida, and I expect Utah and all other states, an individual is always responsible for his or her own conduct - negligent or intentional.  That would place your drivers at risk for liability.

As a lawyer, I would not undertake to prepare a waiver such as you describe without a great deal of legal research and I may decline to advise you at all.  In Florida, liability waivers are valid and enforceable for hazardous activities - such as sky diving, paintball, scuba diving, etc.  However, I have not personally encountered a client, or read a case, involving driving people for hire.  There are strong public policy reasons why a limousine company should not be permitted to avoid liability for its own negligence or the negligence of its employees.  The cost of paying a lawyer to research and advise you about a waiver could well exceed the cost of insurance, and most lawyers will not undertake this task because of the legal malpractice liability that would attach if the waiver did not hold up.

As a practical matter, I would expect people to sue you, your company, and your driver if there were a crash - whether or not you had insurance and despite a waiver.  This would force all of you to hire a lawyer to defend the case - and to defend your liability waiver if you had one.  Quite frankly, the cost of defending just one suit would far exceed the cost of buying insurance. 

I suggest you call several lawyers in your area to find out whether they will advise you on this matter and how much they would charge to do it.  You can start by asking companies in your area that use waivers (try sky diving, ski slopes, outdoor sports, skateboarding parks, etc.) who prepared the waiver for them.  If the cost of obtaining advice is reasonable to you, it is worth getting the advice.  If not, then you are better served to find a way to pay for insurance.  Good luck.