Can a wizard learn a single weapon proficiency (similar to how they can learn a tool set or language, which use Training rules), or are costly and over-blown options like multi-classing, feats, or becoming a Bladesinger the only way?
I know that getting a level of Fighter, or taking the Weapon Master feat, or choosing the Bladesinger archetype would work, but all of these also gain many more things than just proficiency with a sword. They are also either difficult (multi-classing sacrifices a whole wizard level), or very expensive (devoting the character's future to being the Bladesinger archetype), or outright impossible (a DM's game may simply not include the multi-classing or feat options). It seems such a pity when Training rules are right there, but they don't cover learning new weapon proficiencies.
It's possible that I'm fixated on wishing I could just Train for using a sword and I'm overlooking something else.
Is there any simple way that isn't hugely expensive to learn proficiency with just the sword? Is it easier than I am seeming to read it?