Considering the sale doesn't start until tomorrow, it's not surprising that the prices haven't dropped yet.
Anyway, these will be cheapest at Sourcebooks' Discover a New Love club where members will get them at 25% off on top of the $2.99, and the discover15 coupon code may or may not still be working. And they'll be DRM-free MultiFormat there. (Not all books available to all regions, but a good chunk of them sold worldwide.)
Here's their
Discover Georgette Heyer page with the introduction to her works and the suggested reading guide by type.
Mind you, if one doesn't want to shell out the $9.99 for the 6-month membership (which gives you 6 free book credits for selected feature titles and ~40% discount on pretty much everything else in the store), they should be couponable once price-matched at Kobo, and eligible for Books on Board auto-discounts and Rewards bucks.
Several of the Heyers have been offered as freebies previously (and Black Moth is public domain in the US), so one might want to check one's archive before buying.
Myself, I'll be picking up all the romances I skipped last year and any historicals I might have missed. I read all the mysteries last year and if you're morbidly curious as to what they're like, my impressions in the Reading Recs forum:
Inspector Hemingway/Hannasyde series;
standalone mystery/suspenses; freebies
Footsteps in the Dark & Cotillion, which led me to splurging on the lot of the non-romances last year.