Regarding the Janet Evanovich Stephanie Plum sale, it turns out there's an omnibus edition which collects
Visions of Sugar Plums,
Plum Lovin', and
Plum Lucky for just
$8.99 CAD $7.99 USD:
Between the Plums, which is technically cheaper than paying $2.99 per. ETA: and might go to less, since eReaderIQ says it's been as low as $1.99 before, though that was some years ago.
SYKM was very helpful with the reading order, etc., and it looks like the sale might be continuing longer since the pricing there doesn't seem to have expired yet. (I thought I saw a Kobo banner blurb early this morning claiming that list of Macmillan discounts was just for today, but either that disappeared or was just my insomniac imagination.)
Apparently the sale seems to correspond pretty closely to the contents of this omnibus edition:
The Janet Evanovich Collection: The Stephanie Plum Novels (Books 4 to 16 plus four Between the Numbers novels), which is currently going for $57.99 CAD (apparently a sale price down from a regular $125). Only #15 is currently non-discounted in the sale, and if you bought all the individuals after the #4-6 omnibus, and got the non-sale BTP omnibus instead of #1-3 of the Between side-series if it's a better deal in your region, it'd only cost you $42 + $10 to fill the missing #15, which is a pretty good deal, saving you $6 off the omnibus cost.
Unfortunately, #1-3 are priced at an utterly insane $49.99 CAD for
their omnibus edition, though in the US, it's a “mere” $26.99 and hopefully Macmillan will also run another discount sale on it or the individuals at some point for those wanting to start reading at the beginning and not having handy library copies to try.