$275 is only for OCI. This is uniform across all consulates.
For SC, you have to provide $20.00 separately per applicant - If your Naturalization was on or before May-31-2010.
If Naturalization was on or after June-01-2010, the SC fee will be $175.00 per applicant.
If you are collecting the documents in person, I believe there is a provision to do so in Houston, from what I have read (I Belong to the DC thread and cannot vouch for this however).
Last names need not be same. However, full names (First, last) should be consistent across all passports - Indian, US, Nat cert - if required. E.g. If your full name is same in Indian PP, US PP, Nat Cert then you are good. Same for spouse.
If you did any name change during Naturalization, you need to check with the consulate folks on what supporting docs are required for this case.
Good luck