Speakers, even while running for office, are running to represent our country and us themselves. Any politician who is running for office may need to compromise and eventually give up their job, as such they should be financially supported. Ideally, this would be by their job, but I believe that financial assitance should be available for all running candidates if needed.
All Americans have a right to make a living and running for office is an expensive ordeal. If you can get paid while still being able to get your message across, then more power to you! This is a capitalistic society we've created after all. If people will pay you to basically campaign, then you must be worth listening to!
If someone is willing to pay a speaker fee to a politician, the politician should be able to accept the fee, even if they want to use it to fund the campaign. If the free market allows someone to pay a fee for a speech, the person should have the freedom of speech to accept the fee, even if they are a candidate at the time. Candidates still have to eat, so they should have a way to make money. There is no evidence that accepting fees corrupts the democratic process.
I think paying politicians before they are elected has no sense at all. We already are short in money, we shouldn't add more expenses. Politicians in campaign are used to raise their own funds for the elections, it is nothing for them to pay with the help of their campaign drives.