On page 8 of the armory book it states
"If you want to upgrade an existing weapon to be more effective, you can do so by selecting a weapon of the same type and category with a higher level. You then pay the price of the new weapon, minus 10% of the price of the original weapon..."
There seems to be two ways to interpret that.
1) You craft the weapon you selected, so you "upgrade" your handaxe, basic into a switchblade, ultrathin. If this is the case the rule seems useless as you can already salvage 10% of your old item in UPB.
2) You don't craft a new item, you just upgrade the level of your item. You turn your handaxe, basic into a level 8 handaxe, basic (by picking switchblade, ultrathin). If this is the case what weapon do you pick if there are multiple of different values (buzzblade is 9,400. ultrathin is 9,100), can you just always pick the cheapest?