If I wanted a stoplight red stone on the smallish side (3-5mm would be fine) without spending a ton of cash, what specimen(s) should I be looking for? Garnets?
Almost impossible. Red stop light stones are rare in just about all varieties and if they have this colour they typically have a premium attached to the selling price - even small stones. Rubies or sapphires are about as close as you'll get - garnets are very rarely stop light red.
Actually it's easier to find a BE diffused sapphire/ruby in this colour so if you're not fussy about treatments that may be the way to go.
Crud. What if I wanted red - like this guy ( ) - that holds its color? Still impossible? I am fussy about treatments, though not about size (I'd go down to 1.5-2mm range). It's for a rainbow stacker project so I want people to think "red" when they see it. I already have a pinkish stone so I don't want the two to blend together. And I'll be looking for an orange, too, so I wouldn't want it to be too orangish (though I'll probable go for a lighter toned orange so an orange modifier in the red may be OK). AND I need it to not go extinct.
This may hold up the stacker project the way my need for a 5ish mm no treatment ruby is holding up my mother's ring stackers project.
generally his prices are near the top of the market. But I think often, not always, his quality is also near the top. These might be high in the $/carat, but for unheated ruby with nice color and clarity it seems good to me. These appeared on his website at this price a year ago I think. with prices going up everywhere and fast, this price might now be more reasonable. It is a nice project, your stackers. If these dont work for you then you might look at those anthill garnets with the high chromium. litnon and mastercut sometimes has them so you could ask Dana if he has any put away, and Uli has had a few too.
It is actually MORE difficult to find fine colour in such small sizes because the depth (and size) is needed to deepen the tone and saturation. I'm afraid your only option is a ruby because it's difficult to find such a saturated pure red in spinels, no matter the size, especially if you don't want to see extinction and etc.