Well I didn't use the monark forks on mine. Those are suspension forks from a Schwinn mountain bike. I paid $140 for the frame (they marked it down a month after I bought that). The engine kit I got for a steal at $120. I bought a beach cruiser for $40, and got a free mountain bike. Then came all the little incidentals. $17 for a single speed bmx 18t freewheel, $30 ish for the lights, $15 for the mirror, $25 for the battery, $25 for the ammo cans (not pictured), $15 for the speedometer (which broke after a week, so I'm getting a replacement), another $10 for the custom poo poo pipe I built, and add a little for paint, decals, miscellaneous nuts/bolts, etc.
I will say that the diy kits are actually really easy, and it only requires a set of very basic tools to install. However, that bike frame does require you to fully assemble EVERYTHING. The bottom bracket has no bearings, steer tube has no bearings, and lots of parts come in several different sizes. Things like the seat post, forks, and axles all have different sizes that you would have to know exactly which parts to get. I did a lot of trial and error with 3 different seat tube sizes before I found something that fit. So it can get a little daunting. If you absolutely want the in-frame tank and have zero mechanical ability, then buying a premade kit might be your best bet.
The gt2-a frame is awesome though. I'm sure you'll love it.
Welcome to madness
(And thanks, Trey)