This is what the MyMazda.com website says for 30,000 mile service. Not sure if that's worth over $100. Looks like an Inspection, Oil Change and Cabin Air Filter change.
https://www.mymazda.com/MusaWeb/pdf/maint_schedules/2010_Mazda3_MS.pdf
Standard Schedule
* If necessary, inspect, repair, clean, adjust or replace Fuel lines and hoses *2 , Brake lines, hoses and connections , Disc brakes , Steering operation and linkages , Front and rear suspension, ball joints and wheelbearing axial play , Driveshaft dust boots
* Lubricate All locks and hinges
* Replace Engine oil , Engine oil filter , Cabin air filter
* Tighten Bolts and nuts on chassis and body
Heavy Duty Schedule
* If necessary, inspect, repair, clean, adjust or replace Engine coolant level , Fuel lines and hoses *2 , Function of all lights , Brake lines, hoses and connections , Brake fluid level , Disc brakes , Tire inflation pressure and tire wear , Steering operation and linkages , Power steering fluid level , Front and rear suspension, ball joints and wheelbearing axial play , Driveshaft dust boots , Washer fluid level
* Lubricate All locks and hinges
* Replace Engine oil , Engine oil filter
* Tighten Bolts and nuts on chassis and body