I will preface this by saying Fire Trap isn't the most fun build I've ever played, but being able to clear Maven/The Feared for the first time is definitely some of the most fun I've ever had and that more than makes up for any downside of playing a trap build.
I used Ruetoo's fire trap build to clear all content for the first time ever for me in this league, which was showcased on Tripolar Bear's Youtube: https://www.youtube.com/watch?v=u7RvJ02kfvQ&t=6s

Ruetoo's PoB: https://pobb.in/RPigbPyFW-20

Ruetoo has Ashes of the Stars which even now is more than double the build cost. Seeing that I'm a noob and would take me ages to farm I had to adjust the build a little, but definitely still got it working after some time. I wanted to share my build since its fairly different and its that time of the league where people are posting about "end game boss killer builds" and I haven't seen this one come up yet.

My PoB (Level 94) - https://pastebin.com/t4p78VMG
I was going to post a playthrough of elderslayers with height of hubris but my PC is a toaster and I couldn't even record and play without having massive FPS drops, so just check out the Youtube video above for a build showcase.

Pricing of items to get the build going:
Skin of the lords 3R2G1B with acrobatics (non-detrimental mod): 15C (Bought this shit for 2ex week one)
Skill Gems: Lv 4 empower + Lv 5 awakened burning damage + Lv 21 20% qual fire trap = 7.2 Ex (other 3 gems are level 20 20% qual; sub 20C each)
Shield with +2 all res & +1 fire spells = 2 Ex (Kongmings is 1c and probably gives more damage for less survivability from personal experience)
Amulet with +1 all fire and 70+ dex/str: 100C (Found 2 just now for ~90C); 20 attribute catalysts are like 10c and my anoint for +2 max ele res was 125C but you can pick a cheaper one for more damage if you're better at the game than me.
Sceptre with +1 fire spells and open suffix: 25C (50C with 1-2 additional usable damage mods)
Boots (Legacy of Fury unique): 10C (GG tier boots for dirt cheap)

Rings both needs "Non-Channeling skills have -# Mana cost" and as much res as possible. I just upgraded my build and my rings on the PoB cost me 1.5 Ex and 2.5 Ex (two stone, vermillion) but realistically when I first cleared the feared I was running rings with no life and just a lot of res which you can find for much cheaper and craft the mana prefix.
Helmet with life and res and usable anoint: 2+ Ex most likely (although you can go cheap on the helmet stats for a better anoint if needed)
Belt with life and res: ~1-2 Ex depending on how much life you want, getting %life is expensive (my belt was 10 ex, but the %life isn't mandatory).
Jewels with %reduced mana and %life: 5-10C; extra damage is a plus but quite frankly I think all 3 jewels I have don't add nearly as much damage as these were worth. (NOTE: Without these jewels, you have to expend 3 spell points for mana and %reduced mana mastery)

Total: ~18 Ex (Can round up to 20 Ex to have wiggle room on items)

The difference between better gear and budget gear is probably going from 5k to 4k life and 2k ES to 1.5k ES, which is pretty significant but not build-breaking. Damage on this build is super cheap since its all based on gem level really. I wanted to post this because it felt good making a budget version of a build work for me. I don't consider myself the best PoE player by any means so being able to clear all the bosses with this after a few years of playing felt great.