I am not a lawyer.

Ok, so are prenups valid in community property states?

Each state has their own laws, and those laws can change. the simple answer to your question, however, is "yes, generally".

If I have a prenup made in a community property state and then move to a common law state is it still valid? What about the other way around?

Again, each state has its own laws, but presumably yes, if it comports with the laws of your new state of residence. You'd do well to contact a family law practitioner in the new state - you might have to sign a postnuptual agreement.

Do I really need 2 lawyers, a judge, and a video of the whole event?

No, it's a legal agreement - you put it in writing. Each party might need their own lawyer - a family law practitioner in your state can tell you for sure. In any case, each party should get independent legal advice.

How much would all of that cost? (seems rather pricey IMO)

A well-drafted legal document could save you a tremendous amount of time, money and mental anguish later on if things go sour. How much is peace of mind worth to you?

Hiring a lawyer to prevent legal problems from happening is far less expensive than hiring a lawyer to fix legal problems after they've happened.

What usually is contained in a prenup? Is it ok if I write it so that only the money that each individual made is theirs? Can I get rid of alamony?

A judge will generally accept the terms of a prenup, if it is reasonable. They might not if your circumstances have substantially changed since it was agreed to - but again, this can vary by state.

Can I get rid of child support?

You cannot contract out of the obligation to pay child support.