Fun but cheap/inexpensive builds

Brave Lance Galeforce Cordelia is cheap and fun to use.

Or any Galeforce user.

Well, I can name builds, but I need to know what unit (s) we're talking about.

Might be easier if you narrow it down a bit.

But I think that Raven and Lon'qu are great units if you're willing to spent the dew.
Just slap fury, moonbow and desperation on them and they're good offence units.

You might also want to wait and see what the new refines are going to be. 3 of em are on easy to get characters, so they might be worth using if the refine is nice.

Cherche and her Axe are a powerhouse right now. All she really needs is Death blow but even her base +3 Attack will suffice if you want a super cheap but fun build!

Ultimate support Eirika- your choice of boons and banes, refined effect sieglinde, rally res or def, your choice of special, your choice of a skill, vantage 3 or desperation 3, and hone spd 3 as well as s seal fortify def or res. This Eirika is super great support but no pushover and can do damage to opponents when necessary. She can pair well with a dancer.

Blade blast Nino- gronblade+, draw back, your choice of special, fury 3, desperation 3, and your choice of c skill. Her s seal should be picked based on what weaknesses you wish to cover or strengths you want to capitalize on. She pairs well with the previously mentioned Eirika.

All rounder Nowi- + res -spd or hp lightning breath + speed refine, movement support skill, 3 cost special, such as draconic aura, or a 2 cost skill. A skill fury 3 b skill quick riposte 2 vantage or swordbreaker. I recommend vantage tho especially since it can combo with fury. C skill threaten res. S seal should be one that raises attack. With my nowi thanks to this setup she has 52 attack, 33 speed, 33 defense, and 33 res.

Odin with his refine is a fun support, just needs an A slot and desperation. Lucius/Azama with dazzle refined Pain and savage blow make for annoying but cheap to make healers. In addition to Nino, a lot of people forget vanilla Tharja nowadays but she comes with a pretty good base kit.