Reddit mentions of Freya Women's Rio Underwire Balcony Bra, Black, 28DD

I’ll assume you’ve used the calculator and aren’t just guessing your size (if not, please do that to make sure.) Anyway, I’m not sure where to find narrow wires, but going to a 28 band (as you said 30 is too wide) might solve that problem, although I’m only guessing. No clue if it’ll help but here are some bras in 28DD and 28E I found for under $15:

Freya Rio 28DD $13

Panache Idina 28DD/E $13

Parfait Charlotte 28E $15

Panache Elan 28E $15

You could also try searching Bratabase, and may even get lucky with a Ewa Michalak in your price range.

If you have the occasion to come into Quebec City for some shopping, Lingerie Flirt also stocks your size here, they are near Laurier Quebec, close to the bridges.

As far as online stores go, I know Forever Yours Lingerie has a few things in 28DD, but they're mostly the Freya Deco variations, so they probably won't do since you're so narrow.

However the Canadian Amazon has a few options, shipped from Amazon Canada:

Panache Andorra Full Cup

Cleo Lucy Balconnet

Freya Rio Balcony

If you want to dare it, most Freya bras are available in your size shipping from the UK by the Lingerie Outlet Store, they come up at around ~CA$30 each (including shipping) but they are not good options if you are unsure of the model compatibility with your shape.

I definitely agree that options in smaller band sizes and D+ cups are painfully scarce in Canada. It's quite terrible.