I'm sorry, but you're still taking the wrong approach.

You shouldn't say that you need more money due to the cost of living or because everyone else at your level is getting this amount. With that logic, you're basically arguing that you deserve more because everyone else is getting more and therefore you have a right to a certain amount, not based on to the value you bring to the company. This is, by definition, entitlement. In reality, the amount US employees are "entitled" to is the minimum wage. Anything above that is based on the value that employee brings to the table.

To be fair, cost of living and average salary are factors you should absolutely consider when deciding whether to accept a job offer. The fact that you have made a spreadsheet for your expenses and done your research on average salaries is very smart.

However, these factors are not relevant to salary negotiation at entry level, and thus you should not bring them up with the company. Cost of living and average salary levels (specific to industry, position, and seniority level) only become bargaining chips in negotiation when you are currently employed and leaving one job for another, especially if relocation is involved. However, that's not what you're dealing with here.

As I've made clear in my previous comments, you can certainly try to negotiate, but it's a risk because it may affect the way the company treats you in the long-term. As I've mentioned before, it's less likely to effect you if the offer is with a large, well-established company. This is a judgement call you need to make for yourself - you have interned for the company, you know what their culture is like better than I do.

"I really appreciate the offer and I am excited about joining the company, but I do have some concerns about the salary. I would be much more comfortable at $40K, but was wondering if there's any way to meet halfway?"

I think that word track sounds fine, but make sure to cite the reasons related to your skills and knowledge (the things they would not get with another candidate), rather than cost of living or average entry-level salary. They may still not give you the increase you're looking for, but it will make you look a lot better than asking based on cost of living or average salaries.

I'm not going to push hard for it, but it feels wrong to just accept a low-ball salary without at least trying.

I understand where you're coming from - there is a lot of cultural pressure to negotiate for more money regardless of the position/circumstance, especially in the U.S. In reality, entry-level candidates are at such an early stage in their career that the work experience is actually much more valuable than the salary, because it has the potential to greatly impact their career trajectory.