I bought a 40W soldering iron for $4.95 at Crazy Clark's for a temporary soldering job. It was a bit too hot which is what you'd expect at 40 Watts with a tip the same size as a 25 Watt iron but the real fly in the ointment was the silver coloured tip that turned out to be unplated: within a few minutes it was already pitted and looking crook with the solder being burnt by the extra heat.
I found some spring steel rod the same diameter and ground a cone tip on the bench grinder by spinning the steel in the battery drill. After fitting to the soldering iron it runs great: the lower conductivity of the iron tip cuts the heat nicely and doesn't overheat the solder at all, the tip manages to solder fine and only bogs down on a massive join as you'd expect with the lower thermal conductivity. All in all it made an unusable iron into quite a good one.
I'll have to try some other irons I have that need tips that I can't get locally. Dicky's doesn't seem to have tips for their budget irons although the one that might fit, with a shoulder machined on it, is $6.95 or half the cost of a budget iron.