To quote myself in a different thread
Vantec Socket A -- $5 + ship
Link (it's the last one at the bottom of the page) -- it's a small really nice looking blue cooler with a good Sunon fan.. I definitely say this is the best bet for a duron and it's dirt cheap.. I own and have installed several with Durons up to 1000 without any probs.. not for overclocking tho..
Dynatron Microfin Alum Cooler -- 13 + ship
Link -- it's a very good performing aluminum heatsink..
SVC CBG38 Copper Cooler -- 14 + ship
Link -- it's a copper cooler and its cheap.. what more do you need?
ThermoEngine -- $25 Shipped
Link Best damn cooler a few months ago, quiet too.. you could overclock nicely with this..