Just as an addendum to your 5 9's concept - there's a level of stress that comes with providing this, and it's considerable.
You're paying them to absorb that stress and ensure that everything's perfect without having to manage them. It's me saying - I need exactly this, at this exact time, on this exact date, in this exact location. I need it perfect, no ifs ands or buts, no excuses, no reasons, no failures. Perfect. Period.
When providing this level of expectation, when any kind of failure or indeed anything less than absolute perfection is not an option, when there's no chances for do-overs, the stress load that comes with providing that is huge.
I'm not in the wedding planning business, but I'm a service provider in the tech market. As a service provider, if you want me to absorb that level of stress so that you don't even have to think about it, I'm capable, I can and I will absorb all of it. I will shield you from it all and show up with exactly what you ask, exactly when you need it, no failures, no excuses. But you're going to pay for the stress that causes me... and it doesn't come cheap. But it is dependable.
There's a reason you have a wedding planner for your perfect day and they're not just charging you for their planning skills. You're paying them for absorbing all the stress so that you just have to show up and have enjoy your fairy tale day.
You can only live under that kind of stress load for a finite period. Most people crumble in days or weeks. Forget lasting months or years. Eventually everyone breaks. Do you really want to break before your big day?
If you don't want to pay so much, you have to be prepared to throw out your expectations and go for something more relaxed. If relaxed is your bag (it is mine), then you won't have to pay 5 9's prices because you're not putting everyone under the pressure of delivering perfection.