Here are some of my concerns with your proposal:
(1) Only the wealthy can run for office. Of course, this is more or less already the case, but your proposal would write it into the nation's basic law. If outside funding isn't permitted, then that $25,000 needs to come from either the independent wealth of the candidate or from a loan (if that's even permitted). Only a certain class of person would willingly part with $25,000 just to run for elected office.
Only the wealthy can run for office now. But, as I've said, the $25,000 is refundable as long as you get a certain percentage of the vote. All right though, I'm flexible. You can fundraise up to the $25,000 limit for all the mysterious lower-middle-class candidates that don't exist now.
(2) Only the government and major media are permitted to engage in mass political communication. I take your comment concerning "other funding" to include not merely campaign contributions, but also independent expenditures (in light of your earlier comments). So, you would restrict the right to mass communication regarding politics to those who are (a) owners of newspapers and television stations, or (b) government funded. That, in itself, is problematic, but given the concerns I raised in (1), above, it's also clear that you're still restricting this right to the very wealthy.
Right now, mass political communication is limited to the government, major media, and billionaires who can afford to spend millions on political ads. So, yeah, I'm OK with that. Again, you can have a blog. I'm not saying you can't.
(3) Equal funding harms non-incumbents. Incumbents enjoy a significant advantage over challengers, and by requiring equal funding, you make it more difficult for challengers to overcome that advantage. There are a few ways that you could address this problem, though: for instance, perhaps the advantage to incumbents can be expressed as a dollar amount, and the funding to an incumbent could then be reduced by that amount. (You could also increase the funding to challengers by that amount, but it seems like it would better to simply reduce one person's funding than to increase multiple candidates' funding.) Or, you could implement term limits so that, at some point, there is no incumbent.
I'd actually argue against that. In probably 50% of the races, on both sides, there is no opponent. You might have a guy who races $5,000 and has a website from 1998. If even 25 races in competitive districts now have well-funded challengers who will actually make the incumbents work.
Also, along with public financing, there are limits on both when ads can appear (like most of Europe) and how much you can spend. That makes it more competitive so the political ads that do appear actually matter instead of every news ad break consisting of 25 political ads.
(4) $25,000 buys you a taxpayer-funded campaign. What millionaire wouldn't run for office? Living expenses, travel expenses, free advertising, and a many-month non-stop party all paid for by the little people.
Well, like I said, you have to get a certain percentage, you have to give the $25,000 back. But, in addition, I'll write a provision that allows the FEC to fine campaigns and get restitution from campaigns that aren't actually "campaigns."
Also, again, like I've said, there'll be less total political spending because nobody, (except for Cali or New York due to crazy media markets) are spending $25 million dollars on a Senate race.
Oh, and (5) I've grown kind of fond of the freedom of the press, and would hate to see it eliminated. But your proposal essentially does just that.
The freedom of the press isn't limited. Obamaisasocialist.com can still exist. So can the New York Times. You just can't carpet bomb 50 30-second ads right next to a Tide commercial for three months straight.