A bill must be passed in identical form by both house & senate before it can be signed by the president. So 50-60 bribes could still be used to prevent new legislation, but much more money would be required to promote new legislation. Increasing the house size (growing w population, 1 rep per max 30,000 people as was once the case) would have likely prevented lots of the policy atrocities that have been passed in the last ~100 years. The electoral college is based on the number of congress members, so it would also limit the likelihood of the elected president losing the popular vote.

I’m surprised by how little money it takes to buy senators.

The whole concept of "buying" a politician isn't a very truthful way to frame what happens anyway. No politician votes in a way they weren't biased towards already just due to campaign contributions.

Indeed; people and organizations just contribute to the campaigns of people who already happen to support the policies that benefit them. Sometimes there's a sense of reciprocity, and sometimes there's small-scale corruption (e.g. Corporation X donates money to the campaign of Mr. Congressman, who in turn votes for an appropriations bill where the Pentagon orders 10 million units from Corporation X), but it doesn't seem to influence individual opinions on broad-scale policy. It's not as often that people get elected on an animal rights platform and then start taking money from Big Fur and turn around and vote for clubbing baby seals or something like that. Big Fur just saves their money and donates to the pro-seal-clubbing candidate in the first place.

It's less to do with the fact that they're accepting money from causes they are sympathetic toward and more related to the fact that they are now under an obligation to continue supporting the causes they've received money from or stop receiving donations, against the wishes of their constituents.

See, for example, the tax bill of 2017.

In your experience, what was the price you had to pay to buy a majority?