Gotcha, yes....no budget! Sounds like where I work.
A TL082 is a nice sounding chip and can drive just about anything.
I have built circuits similar to the one's in the link below using TL082 and the OPA2134

http://www.all-electric.com/schematic/simp_mix.gif

 

A TL082 is a general purpose dual Jfet-input opamp. A TL072 is the same with the same price but it is selected for low noise to be used for audio.
The OPA2134 dual opamp has much lower noise but it costs much more.

 

Gotcha, yes....no budget! Sounds like where I work.
A TL082 is a nice sounding chip and can drive just about anything.
I have built circuits similar to the one's in the link below using TL082 and the OPA2134
http://www.all-electric.com/schematic/simp_mix.gif

Thanks for the link. Why is is that this schematic uses two op-amps, while the ones featured at http://sound.westhost.com/project94a.htm only use one? Which design is better?

A TL082 is a general purpose dual Jfet-input opamp. A TL072 is the same with the same price but it is selected for low noise to be used for audio.
The OPA2134 dual opamp has much lower noise but it costs much more.

Noise isn't terribly important. It's going to a radio transmitter, and even with perfect sound going into it, it sounds a little staticy on the receivers.
It was a tossup between the TL082 and the TL072, and I plan on using two TL082s just because I already have them.

 

The mixer is an inverting opamp. A second opamp inverter can be added so that the signal is inverted again so it is not inverted anymore.

But most of the time the phase doesn't matter as long as all channels are treated the same because you cannot hear the phase difference.

 

Ditto from Audioguru's comments.....I generally use this circuit or one typically like it, but one opamp is all that is needed.