Building and fine tuning a DMR isn't that simple compared to HPA that's for sure. And you can adjust a hpa on a whim it's just way more comfy.
I'm sure polarstar has some engines where you can attach a CO2 capsule or tank. Also, if you have deep pockets you could still buy an used MTW and buy a wraith stock later down the line.
You can buy carbon fibre tank for silly money if weight is a real concern. Altough those cheapo 13 CI tanks weight literally nothing so it shoudn't be a big problem.
Personally I'd spent the least of money on this adventure because if you don't enjoy it at least you're gonna lose less money on it if you resell it. You could buy used HPA kit or gun as well to be honest.
I'm an avid HPA player but outdoor can be problematic because of the line.