Yeah, at most a +1 weapon. Seriously, it works. I usually factor gold into the following:
1/4 to offensive gear (Weapons, ability boosters, pearls of power for casters)
1/4 to defensive gear (shields, armor, protection items)
1/4 to expendable income (wands, staves, scrolls, potions, etc.)
1/4 to miscellaneous costs (spellcaster services, advanced healing, tolls, mundane equipment)
I figure at most you could rule up to 1/3 total gold to any one item... but that stills makes a LOT more things available to characters of that level (+2 ability boosters, high level wands, etc). And if you have a magic item crafter... they could have REALLY good gear at 6th level.
But, back to the main topic, actually, I'd give the Legacy Weapon user a 20% discount to costs of his item. Why? Because they're set in stone, they can't be sold individually, you can't trade up to a better one mid-level, and one Sunder and you've lost a REALLY powerful item.