Car won't start

I really hope you can help me out. I have a '98 Pontiac Sunfire 2.2L that turns over a few times but won't start. I have replaced both the battery and the starter.

When I put my multimeter over the brand new battery, I get around 12.5 volts when off, but when I turn the key to "ON" and attempt to start the car the voltage drops to around 7.1 volts. The engine will turn over a time or two. If I try starting it again, it may turn over once or not at all.

Any idea what could be causing the voltage drop when I try to start the engine? I am thinking that because of the low voltage the starter isn't getting enough power to start the engine.

I can confirm I am getting a spark, and the alternator is roughly 6 years old.

I really appreciate any help you can provide.