No way you're going to get those for cheap. They're wideband sensors.
The only possibility is swapping in some generic Bosch wideband sensors, which are about $100/piece.
May I ask you what's wrong with yours? They're covered under the emissions warranty of your car, and ought to be replaced for free even if you have mods.
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'10 PW 370Z 7AT - wife's car - Project Raspberry Cheesecake
'08 Evo X - built motor+trans | BB-X @ 32 psi | CH3OH | self-built+tuned - ??? WHP
'01 Galant V6 - built motor | GT35R | self-built+tuned - 550+ WHP (retired) |