I noticed the flag was tangled at the top of my 25-30 foot (not exactly sure) flag pole. I was taking it down and the rope snapped. How the heck is the best way to get to the top of the pole to run a new rope through the thing at the top. is a ladder with someone holding the bottom the best way?

That's the easiest cheapest way. Unless you have a friend with a boom truck. I'm assuming you don't have one of those that fold over.

You may be able to do it with a ladder but I don't believe that you can do it safely with a standard ladder. In addition to side to side movement concerns, is the pole of sufficient strength to withstand the load of the ladder and you, not knowing how much of you there might be (150 lbs or 275 lbs, more or less or in between). I am also assuming that the rope came completely out of the top pulley? If not you would have other options. If the rope is just broken but still accessible through the pulley, this is the procedure: How to re-rope a flagpole, rerope a flagpole
Another option if you are as fit as the guy in the video: FlagRunners: How To ReString a Flagpole Without a Lift Truck - YouTube
Best choice (if rope is totally out of the pulley): A boom truck or rent a manlift (probably less expensive than you think) and yes, you need a safety harness with any type of lift.
If you insist on doing it with a ladder, get plenty of manpower (minimum 3 strong adults) to assist you- and make sure you have insurance- sufficient insurance to cover you in a bedridden condition for the rest of your life. Don't gamble when the results can be catastrophic.

There are work platforms that extend up to 30 feet with all controls on the platform. If ground is flat it may work for you. A lot cheaper then a bucket truck.

Chuck