Tanzanites come in a variety of blue to violet shades so it would be helpful to get a clear description of colour; attaching a picture of something that inspires you is best (be it sapphire or tanzanite). Based on that, the regulars here will then be able to advice you on the approximate price range in the sizes you are looking for. 7 mm translates to something of nearly 3 carats and a stone of around 10 mm has to be at least 6 carats, give or take since this is only an approximation.
I prefer tanzanites that have less blue, like the one in the picture. The top is kinda of dark. The brighter area (bottom right) has the color I want to get; the color could be a little more intense.
I prefer tanzanites that have less blue, like the one in the picture. The top is kinda of dark. The brighter area (bottom right) has the color I want to get; the color could be a little more intense.
Based on the ring you've shown, I would suggest you look for a violetish blue sapphire rather than a purple sapphire. I've spent years finding the perfect purple sapphire - they're either too pink, too blue or too amethyst looking and actually much more difficult to find in "your" preferred colour! If you like (generally) the colour of Tanzanite then looking for a sapphire that has a lot of violet or purple in it may well fit the bill.
The only other thing I would say is that Tanzanites (good ones) are very warm and rich looking. To get that in a sapphire will bump the price up a bit.