You have the triple constraint theorem here - cheap, good, fast. Pick any 2. I can also quote Ruskin: 'It’s unwise to pay too much, but it’s worse to pay too little. When you pay too much, you lose a little money — that is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing it was bought to do. The common law of business balance prohibits paying a little and getting a lot — it can’t be done. If you deal with the lowest bidder, it is well to add something for the risk you run, and if you do that you will have enough to pay for something better'.

You have the triple constraint theorem here - cheap, good, fast. Pick any 2. I can also quote Ruskin: 'It’s unwise to pay too much, but it’s worse to pay too little. When you pay too much, you lose a little money — that is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing it was bought to do. The common law of business balance prohibits paying a little and getting a lot — it can’t be done. If you deal with the lowest bidder, it is well to add something for the risk you run, and if you do that you will have enough to pay for something better'.

Many Chinese company offered a very good discount on different substrates. Please check

I would also recommend the Chinese market. I recently got invite from them and I think you can get a relatively good deal from there. And please do keep Alan's comment in mind.

Cheers

For quartz substrates you may contact atslab....

http://www.tcichemicals.com/en/in/

https://www.universitywafer.com/thermal-oxide-silicon-wafers.html

I like Alan Rawle's philosophical sensible answer. But we all seek the best deal. Now we have the world at our fingertips we can find the best product supported by the comments of others hopefully. It is tough on sellers but essentially it is a buyers market at last. The days of a 'pig in a poke' are hopefully over. But 'buyer beware' still applies!