Cel With Numerous Codes - Help...?

Hi, I have a 1999 Mustang coupe with the 3.8 v6 and 5 speed. A Craiglist special.

Yeah, it's not some showroom classic, it's just a fun little cruiser - I hope.

The car runs poorly - it runs at 2000 rpm always - and when I attached a scan tool to the car, it shows these codes:

P0443 - Evaporative Emission Control System Purge Control Valve Circuit
P1451 - EVAP Control System Canister Vent Solenoid Circuit Malfunction
P0412 - Secondary Air Injection System Switching Valve A Circuit Malfunction
P0135 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
P0141 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
P0155 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
P0161 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 2)
P1409 - EVR Control Circuit Malfunction

From reading other posts on these forums, it appears that these codes may be masking the actual problem, but I am not sure where to start.

I'm sure it's possible that all four O2 sensors failed, but is there a way to test before I start spending all kinds of money on sensors and other stuff?

Thanks in advance.