I'm actually on the same boat as you.
I've been to Spence, Birks, etc, and I've done my research. I have found the place I will get it - it is going to be custom made; copied to ANY ring you want (Tiffany's, Birk's, etc). And it is the cheapest place I've ever seen.
This place is called 'Diamonds for Less', and apparently the reason why they're so cheap is because they ARE the wholesalers - they completely cut out the middle man.
Eg - for a 0.70 karat, G colour, VS1, excellent cut at Birks, i'm spending more then $8,000 (no joke).
For Diamonds for less, I asked for a 1.00 karat, E colour, SI2, excellent cut, he's giving it to me for $4,500 ($1000 extra for wedding band). Look at the savings vs. the quality - big difference!!
Anyhow, you can check my other posts, I'm not advertising these people, I genuinely think they're the cheapest out there - Just tryna help a fellow terbie out.
Let me know if you need any more info.