Synthrotek seems like a best bet if you're going to DIY your skiff somehow. I think their current green/red/blue Super Power setups offer a nice, easy integrated solution, since they tandem with their Noise Filtering busboards. Or, you could just go with a small case that has the built-in power from them as well; a 4U portable case also offers a 1U row for utility tiles (not the Intellijel format, tho) that can increase functionality on basics for cheap.
Dynamix might be a bit pointless, since my take is to go with something denser/cheaper. MATHS, however, is NEVER pointless. It's nothing but sheer CV functionality in 20hp. Do consider an LPG of some kind for easy timbral/dynamic control in a tight hp situation, though.
As for cost, I've used the following rule-of-thumb for quite some time in figuring Eurorack (and other) format cost control:
PRICE / hp = cost-per-hp.
The lower you can make that resultant product from that equation and still get the bang-for-buck you want, the better. This also predisposes one toward more sizable panels, but this isn't always the case, and the end-result isn't generally so control-dense that it makes navigating a patch and working with it in realtime a hideous chore.