It’s perfectly possible, since it’s roughly what is done over here.
Some rules about french elections :
-The amount of donation to political parties or candidates by a given company or individual is limited to a low amount. It means in particular that a particular corporation’s contribution can be really significant.
-The expenses during a political campaign (there are official dates for the beginning of the campaign) are topped. If an elected candidate has spent more that the allowed amount, his election is cancelled. Courts handle dubious case (for instance, an election has been cancelled because the leaflets had been printed for free, and the real cost of the printing would have resulted in the expenses being above the allowed limit). Books have to be kept and are controlled by magistrates.
-The expenses of a candidate or party are reimbursed if he/it get at least 5% of the votes, up to a given amount (which is lower than the maximum expense allowed)
-Political ads are forbidden at all times (whether there’s an incoming election or not) on all broadcasted medias (TVs and radios).
-During a campaign, broadcasted medias, public or private, must offer an equal time to all candidates. For instance, if a famous politician running for a local elected position is some remote place is interviewed, then the other totally unknown candidates for the same position have to be granted an equal time. Sometimes, it results in a lot of interviw of fringe candidates towards the end of the campaign in order to “fill the quotas”, since it’s very strictly controlled. I’m simplifying here, since it’s more complicated than that, it depends on the election, members of the executive can have a specific quota for political expression, etc…
-There’s an “official” campaign on public TVs and radios. During the presidential elections, each candidate is granted exactly the same time of broadcast, that he can use as he see fits (make a speech, broadcast a political clip, etc…). During other elections, it’s parties, instead of candidates which are given an '“expression time”. Parties represented in the parliament benefits from a much longer time than parties which aren’t. They also have to present a minimum number of candidates (for instance, you can’t found you own party, run for mayor in a remote village and claim an expression time on public medias).
All these laws are (obviously) intended to level the ground between candidates and to insure that their financial ressources will have only a limited influence re. their capacity to be elected.
(also, publishing the result of pools during the week preceding an election is forbidden, but the intend of this regulation is different and it became for the most part a moot point with the advent of internet).