The filing fee in South Carolina is so large because the state parties pay for the primary there, and the state GOP wants to recoup at least some of the cost by making the candidates pay through the nose.
In most states, the state government pays for the primary, and so the filing fee is much smaller (a few hundred $ in most cases, I think). However, they also tend to require you to produce a bunch of signatures, so unless you have a huge amount of organic support, that also requires you to spend some $.
So candidates with little to no money could indeed end up being left off the ballot in many states. We'll just have to wait and see how it goes.
South Carolina funds the presidential primaries. It lets the parties set the date for their primary, and also to charge a "certification fee". The state may charge a filing fee of up to $20,000 per candidate.
There is at least a possibility that the $40,000 fee is unconstitutional.
Texas primaries are (nominally) conducted by individual parties, but funded by the state. At one time, the parties were required to fund their primaries from filing fees. Filing fees for some offices, particularly statewide office, were set in statute, but filing fees for statewide office split among 254 counties don't go very far. The county parties, who conduct the primary in their county were required to charge filing fees to county offices to make up the difference. Some ended up charging exorbitant fees (if adjusted for inflation, some would be over $50,000).
The SCOTUS ruled this unconstitutional (
Bullock v Carter ), reasoning that if violated equal protection of the right to vote (it was reasoned that poor voters might support poor candidates). Since then, the state has funded the primaries, and also sets the filing fees.
The primaries are still (nominally) conducted by the parties, and candidates file with their respective parties. When the parties send their expense report to the state, they deduct the money that they received in filing fees.
Texas does permit parties to set the filing requirements for presidential primary candidates, and they are different between the parties.
The GOP charges $5000, which is the filing fee for US Senator.
The Democrats charge $2000, and require a loyalty pledge (in 2008, Dennis Kucinich refused to sign and was left off the ballot).
Both parties also have a petition alternative, but unless someone was wanting to demonstrate their grass roots support, the filing fee is cheaper. Since filing is in December, a grassroots effort in Texas would be taking away from organizing in Iowa, for example.
The Democratic National Committee has a cap of $2000, so it might be that the SC Democratic fee is much less - or it is conceivable that there is some loophole.
