Hi Stefanie,
I’m sorry to say but I don’t agree with searching for the cheapest possible supplements in general. You normally get what you pay for.
There’s a saying that if there’s 3 things in life you should never skimp on they are: parachutes, scuba diving equipment and supplements.
Obviously you don’t want to pay too much money but I would consider not spending minimal amounts. I have heard Poliquin’s supplements are good but I think some of them are pricey.
Hope this helps,
Rob.