He's in a good bit of events, but there are a few factors.

How many you get for free is one of them, in mission boxes, at the moment, you can get a total of 12.5% of him, or 10 fragments, for pretty much free, as long as you do all 10 missions daily. (And you'll be halfway to one extra fragment), so it's best to go after him pretty much whenever, that'll help lower down the final price.

His price varies through events, but Herz has covered that part, my only suggestion is to be sure to pick up whatever free frags you can.