I agree with John, any time we can
reuse plastic, we must do it to keep it out of
land fills.
As far as the high cost of pre-made Ollas;
If you can buy clay or dig your own, you could always make your own vessels.
Making your own allows you to shape them to your needs. All it takes is clay, rolled into a "rope" shape, coiled up and then worked into a monolithic form, smoothed with wet hands and if you like, decorate with your totems or designs.
Let the ollas dry for at least a week, two is even better.
Place them in a fire pit, on a bed of twigs and build a fire stack around them so the pots are inside the fire stack, light it and fire the pots the way the ancestors did.