I encourage you to check out what Evan (on of the HarvardX staff members) put out about how you can get the BOM directly: TinyML Hardware Kit - #38 by jesmith. It talks about how to get the individual parts if needed. One reason we put this together is because the cost can be cheaper when you cut out all the headaches with shipping and custom fees etc. All of which was well out of our control 
Anyway hope it helps folks looking into getting parts for the long run. I strongly encourage folks to get the kit just cause we have tested everything using it.
Yes, and no. You have to change the code a little bit to get it working. We in fact provide instructions on this as well in Course 3 just in case people aren’t able to get the OV7675 part… but again, prefer if people use the kit just cause we know it all works and we have shipped an Arduino library as well that has the necessary tests. etc.
Cheers!
I am looking forward to all the projects that will hopefully come out of doing Course 3! 