@IntoBerkeley Hi There!
To answer your question, applying to regular decision doesn’t exactly reduce your chances of getting in, but you’ll just be compared to a different pool of applicants. If you complete the application to the best of your ability, then you can have a good chance of getting in.
Just like applying to college financial aid, the amount given depends on your financial situation. To quote from SSI:
The Summer STEM Institute (SSI) provides financial aid for families and students who cannot afford to pay full tuition. Cost is not intended to be a barrier to participate in the program. Students and families in need of financial assistance are encouraged to apply for financial aid.
Be sure to complete your application, then follow instructions listed here to complete the financial aid process within three days.
Finally, alumni and myself included have posted our honest experiences in this thread for potential applicants to read.
I hope this helped!