I suggest you get a very decent mono Montana deck for 3500.
2* Filomena 200
2* Prince Jr 700
2* Ricardo 200 (change to Edd later)
3* Simon 250
3* Giovanni 300 (change to Mona / Ottavia later)
3* Sharon 300
3* Oscar 300
5* Don 1200
Well you can certainly make a decent half deck for around that if you don't mind taking a 2* that is good but will later be upgraded;
Otakool ~ 600
Lolly ~ 600
Dash ~ 750
Onik ~ 900
But as for a mono deck, whilst quite doable with junkz I think I'd rather keep them to a half deck and there is no way you're going to be getting a good mono deck for that cost as Gil and Veenyle are pretty vital to it along with rowdy, gibson etc.
Mono Junkz is indeed very difficult to play (low dmg DOES NOT help) and I sincerely hope that there will be new good cards for Junkz, however you can do well with Junkz and find yourself in top100 in DT if you play it with some love
First things first AWWWWW LOOK AT THE PUPPY!
now then, to start you off, some good/ok cheap junkz are:
do not attempt to go mono-junkz, they are hard to work with