Progressive titles almost never include a purchase option, because a guaranteed feature entry would undermine the funding model behind the pooled prize. Coverage at https://thebonusbuyslots.com lists the few local jackpot games that do allow it and how they adjust the contribution rate. Most studios keep the two mechanics apart entirely, which is why you rarely see both promoted on one game. Not a restriction that bothers me, since jackpot maths is already awkward.
