@Donmikan - You're probably not going to find the same level of playability from any Pro's Pro string, as most of them have simpler formulations, extrusions and finishing. That said, if you're going to try a Pro's Pro string, the closest to RPMB would be
Pro's Pro Strategem 8, as it has the exact same 8-sided "flower petal" type cross-section and silicone coating on it -- clearly meant as PP's RPM clone. However, in looking at all the feedback on PPS8, it seems to experience a larger initial tension drop than RPMB, so you'll probably want to either string it with a 5 or 10% pre-stretch, or if you don't have an electronic machine, simply do double-pulls and/or increase the reference tension by a couple pounds/1kg or so.
Beyond PPS8, I would recommend looking at
Gosen G-Tour 1 -- despite being fully round in shape, it has very similar playability to RPMB, including a silicone oil infusion; while I find it doesn't offer quite the same level of wild/crazy spin up initially, the level that is does offer tends to stay more playable for longer, and it's roughly half the price (street price as cheap as $10/set and $97/reel). You may or may not get 20 hours out of it, but IMHO it's definitely worth a try. I'd start with a set or two and give it a shot.
Hope that helps. Any questions, feel free.