Don't use any wood chips with tarantulas at all is best, but if you must, make sure it is a hardwood. All evergreen trees contain a natural insecticide.
Peat moss is what most use and you'll find it in any garden store or dept., and it is likely cheaper than the wood chips you are talking about. I us it mixed with vermiculite, but some Ts once grown, are fine without it's moisture retentive qualities
I use the shredded coconut bark for my T's, this and organic growing medium come in bricks that you soak in water to expand it and break it up. This stuff is good because it gets lighter in color as it dries out and you can see if the enclosure needs more moisture. When it's dry, it is just like dry dirt when it comes to cleaning it up. Use something like this and stay away from the wood chips and the gravel.