Lv. 10 unevo'd Pengdras provide 6,000 Exp, or 9,000 for on-element fusion.
Evo'd Pengdras provide 30,000 Exp, or 45,000 for on-element fusion.
Despite how huge the boost is when evolved, though, it's MUCH easier just getting 5 normal ones and using them instead of trying to evolve one, unless the corresponding jewel urgent dungeon is active at the time or will be soon after the Pengdra hunt. More expensive coin-wise, of course, but worlds easier.