In the US do you have anything similar to the UK's electoral commission?
Its basically an independent watchdog which all parties need to report all spending to, the data is then published online for citizens to look at. They don't have to report anything less than £200 though.
Also, we have spending limits. For the general election it tends to be about £30,000 per seat (a seat is basically a constituency) so if they're after every seat it works out at around £19,000,000 as the total legal spend.
That being said, I think the 2015 election had spending of about £37,000,000 ($50m) for all parties.
What was the US election? $6.8 billion?
You also never really see TV ads, we have 'party political broadcasts' on BBC One in the lead-up to elections but they come preceded by 'This is a party political broadcast by the Conservative Party.' What this does mean is that our politicians spend ages walking around various shit towns across the country pointing at things, eating local cuisine (bacon sandwiches, pasties, etc...) and being condescending towards locals.
Its a very different system. I'm not saying there's not corruption but it blows my mind that these people are so brazenly bribing your politicians with 8x the amount of money another Western, First World country spends on their elections.
https://en.wikipedia.org/wiki/Citizens_United_v._FEC