Budget Build for Roderick

His base kit is pretty good already just give him an a slot like L&D 2 and draconic aura and you're good.

A cheap option would be something like Luna, Darting blow or Life and Death 2.

Weapon Skill: Firesweep Lance+ (Default)
Support: Rally Def/Res (Default)
Special: Luna (Can't think of a super solid reason to use anything else)
A: Darting Blow: (When initiating gets your speed up to 40)
B: Drag Back/Hit and Run (If you were to use him to rush in he can get a space away, but other B skills work aswell, also drag back is default)
C: Drive Defense 2 (Default)

You also have the option of inheriting his lance away to a powerful flyer like cordelia