If the Marine is living off base they get a food allowance – $202.76/month for officers and $294.43 for enlisted
The housing allowance varies by region and I didn’t find numbers for San Diego county
Perhaps the income numbers above aren’t so bad if your rent or mortgage is also paid by the military
~
As far as the Marines supporting the local economy – talk to some business owners and/or landlords in Oceanside about their economy when the Marines are deployed