Valter

He already has Swift Sparrow 1 with his default 5 star weapon, making Swift Sparrow 2 give him Attack/Speed+6 every time he initiates. With his high attack with his lance and Swift Sparrow, Vantage would let him attack first, and just in case he can't finish the job, Threaten Defense/Draconic Aura ensures he does. Pivot also lets him get in enemy's way, which with his high defense and attack works well for him and his team.

Valter's attack and speed might not seem like much at first but the boost from his cursed lance adds both attack and speed by 2 making it 34 attack and 33 speed plus with Life and Death 3 it becomes 39/38 making him pretty powerful and with the mt from the Cursed Lance it becomes 55 attack and 38 speed and also thanks to the cursed lance moonbow will take only one hit to charge. And this makes it so that most of Valter's opponents will die as long as he doubles them.

Rough Moonstone, a budget Valter guide.

With Cursed Lance, Valter effectively has 50 Atk and 33 Spd. This makes Valter a pseudo-physical tank with above average damage potential. Because of his lackluster Res stat, make sure to avoid magic units, especially ranged ones because they will deal a free 4 damage every time due to Cursed Lance.

Darting Blow 3 is the default Passive A for Valter, and doesn't need to be changed. On initiation, Darting Blow 3 will boost Valter's Spd to 40, allowing him to easily double most foes, especially if additionally boosted by a Spd Passive C. Note that most units will not survive two hits from Valter, and if the enemy can counter-attack, Valter will proc Luna on his 2nd hit (assuming a special trigger countdown of 2 on initiation) and KO all but the most defensive of foes.

Vantage 3 is the preferred budget Passive B for Valter because of his high Atk and Def stats. High Atk is beneficial because it means Valter will either heavily damage a melee attacker before being hit and/or killed, or straight out kill them first. His high Def stat works well with Vantage 3 because Valter will take minimal damage from physical, non-axe foes and proc Vantage more often simply due to surviving longer.

For Passive C, you can either stay with the default passive, Panic Ploy 3, or, as I recommend, Threaten Def 3. Threaten Def 3 further improves Valter's ability to KO enemies, and if doubling thanks to Darting Blow 3, means an additional 10 damage on debuffed opponents. If you plan on using Valter in a Flier Emblem team, you should obviously choose any of the Flier Passive C skills, but seeing as Flier Emblem isn't exactly "budget", I won't go into detail on that.

Cursed Lance is an incredibly strong weapon because it combines the 16 Atk given to unique melee weapons, Fury 2 without the Def and Res benefits, and the effect of Killer weapons (-1 special trigger countdown). There is no better budget alternative.

As with all hero builds, the chosen Support Skill is mostly due to preference. Another popular Support Skill, such as Draw Back, would work fine.

Luna, often overshadowed by its faster counterpart, Moonbow, is amazing on Valter because Cursed Lance reduces the special trigger countdown from 3 to 2. As explained above in the Darting Blow section, if Valter doubles an enemy that can counter-attack, he will proc Luna and more than likely kill them.

Playing to Valter's strengths, while being mostly cost effective as far as SP goes. His already high defense gets a massive boost past the 50% HP threshold - higher than stock Hector. He's weaker to bows and mages, as per the norm, but pair him with a healer and he should be able to chunk anyone down. Being able to take a lot of hits in a melee brings Luna up quickly, and as it's Luna, you don't have to worry about Valter not having enough ATK to get through certain high defense greens. You shouldn't have to worry about them anyways, if your team is balanced fine.

With Reciprocal Aid, you can make the most out of a Rehabilitate or Martyr healer by trading off the low HP and healing, considering Defiant Def lasts until the next turn. You could have a full health Valter who still retains the Def buff. And that's not even considering Spur buffs.

Valter's decent base speed paired with Cursed Lance's passive and Darting Blow will allow a total speed of 39, which is good enough for desperation.

Reposition is a must on any flier since allows infantry units to go over obstacles like mountains and rivers.

Guidance will further amplify his support ability.

Luna is a good enough trigger for him, especially since it will have reduced trigger.