Hi! Just my 5 cents:
(1) I didn't try these Germans:
https://tapemuzik.de/ but they do have type II, custom lengths and custom shells, also sell cases, and seemed slightly cheaper than tapeline was;
(2) tapeline seems to have moved their bargains to ebay (though they will prolly tell you that anyway) so I second deutcheasphalt's point; also recently got some unused type II C90s from Spanish ebay and they are nice, though that's just as you said, just have to wait for the offers of 50-100 (that's one thing their annoying alerts _sometimes_ do help).
(3) Oh yes, one more thing: tapeline offers superferric tape only now, which is claimed to have slightly better characteristics. Maybe worth giving it a try? I only have one (and ~8 ferrics from them) so I can't do any comparison for you right now...
(4)
http://stereostyle.pl -- but you have to email them to get any prices. They do answer quite fast though, also (just as tapelike nad tapemuzik) do polygraphy [quite nice] and duplication [okay-ish]. I paid ~110eur for 30 (type-I) cassettes with one-side print and glossy o-cards with printing. it's significantly cheaper for 50+ cassettes and for plastic cases ofc. but that was last year, so just check if you're curious. small choice of shells but you should be good (with plain white or black I suppose). I guess I'll use their services once more anyway...
(mind that if you are outside of EU you might be charged some customs fees for those 3 though)
Also my [tiny] experience is if you are more into low hiss level than sharp/clean sounds and duplicate at home, try recording slightly hotter signal, like +3dB (and use dolby B, there are hardly any players which don't offer it and it does quite a good job) -- I was amazed it's not necessarily badly distorted. But I'm a half-deaf ignorant too and I record lengthy ``drone walls'' only.
Last thing:
(5) I was advised to avoid tapes from aliexpress, though prices are attractive at least their ferrics leave a lot of dirt on heads/pinchrollers...
Good luck, last December tapeline did offer a pack of 40 or 50 type-II C20s, so it does happen!