Disregarding chase mythics, every deck is pretty cheap. At least here in Europe. Just look at this es.magiccardmarket.eu/Home/Featured_Products
BG Energy doesn't get affected too much for the rotation. Most of its creatures and cards come from Kaladesh block. Just switch the trackers for a Rhonas and some elephants for example and those token Khirans for Aetherspehere Harversters for a better budget. The only thing expensive in BG Energy are the Fatal Pushes (which you have already), the ballistas and the beloved Gearhulk, which can be substituted by a Ridgescaled Tusker. I know, it is not the same as a Gearhulk but it can do the job more or less.
Other arquetypes, rotation proof, are Mardu Vehicles, Temur Energy, Mulato Zombies, UR Control and New Perspectives. UR Control is pretty cheap, really, if you switch the gearhulks with some Enigma Drakes. You won't put them out until you see the enemy's hand reduced to zero, anyways.
Here, in the city I live, there is a very competitive meta and, surprisingly, I reached top 4 of the FNM league of the ENTIRE city. I didn't get to win anything because you only get a prize for the first position but, thinking about it, it is surprising when you budget a little against the opponents.
The deck I am using right now is this mtggoldfish.com/deck/680399#paper . Pretty cheap, really. Mythics are only one of two of because are the ones I got by cracking packs won at FNM. In practice, Kiran and Hazoret are just removal bait, while I strive to get the upper hand in tempo with Authority of the Consuls so I can beat my opponent with dwarves and cars before he can even use a blocker.
The sideboards is heavily against Temur Marvel and I preffer to mainboard magma sprays rather fatal pushes, which can make you realise how much of netdeckers are at my LGS,bringing a lot of Temur Marvels and Zombie Decks. I have yet to modify the sideboard but I am in finals and last Friday was my last FNM until holidays