yes you can apply to multiple specialties, actually this is adviced to be done to gather the highest number of interviews. you can upload from your computer as much personal statements as you want but you can assign each program only one.
you can apply to neuro when you are in IM but the issue is that you will need a LOR from your current PD. Usually they will give it to you but I don't think you will be in good shape if you didn't match with another program.
Regarding the cost, it is calculated per specialty as follows (see also the examples below):
Number of Programs
Per Specialty ERAS Fees
Up to 10 $75
11-20 $8 each
21-30 $15 each
31 or more $25 each
Samples of ERAS Fees:
Scenario1: An applicant applies to 30 emergency medicine programs, total fees are $305. ($75 + (10 x $8) + (10 x $15)).
Scenario 2: An applicant applies to 20 OB/GYN programs, and 10 family practice programs. The total fees are $230. ($155 for OBGYN and $75 for family practice programs).
Scenario 3: An applicant applies to 23 internal medicine programs, and 7 radiology programs. The total fees are $275 ($200 for internal medicine programs and $75 for radiology programs).