For the most part any clan can be mixed with another, except Rescue, they should always stay mono. Now some clans do compliment clans more than other clans would, but since you already have GHEIST and Freaks , a good starting deck would be:
Dolly , Mok , Anibal , Mini Mund , Bertha , Igor , Karmov , Quasichoco
Play some tournaments, rack up clintz and credits, ??? , profit
Shedding insight on what previous people have said:
Richliu's logic is quite good. If you're trying to get the most out of your deck, running mono Freaks is slightly suboptimal, as they are essentially bonusless in the last round (and often the 3rd, too, depending on your opponent's life totals).
Adding a few more options to Gomla's recommendations:
Try out Shazam, who is an amazing 2* for Freaks. Eve is probably the best cheap 5* in Freaks available... Once you save up enough money, the Freaks staples are Bogdan / Grudj, Olga, Shazam. Madelone, Bertha, Esmerelda are all strong options as well.
On the GHEIST side, add on Bristone, Hriger, and Ksendra as solid upgrade cards to look at for starters.
I'd ditch GHEIST altogether if you're looking for cheap cards. Freaks low star cards and some of their lesser five stars are quite cheap (Bertha, Shazam, Wonald off the top of my head) but their best cards and staples are four stars that cost a hell of a lot (Bogdan, Grudj mostly). Try a low star Freaks half deck with another cheap clan half deck.