Several generic versions out there - Dutas & Duprost spring to mind - and a small army of (quite easily found) websites happy to take your custom.
As for genuine Avodart... the cheapest source I know (except from an actual doctor) offers 90 capsules shipped to your front door for 140 Euros. Which is around US$180.
Sorry... generics: unitedpharmacies.com and inhousepharmacy.com are the two biggies, used them myself numerous times - mainly Proscar for my dad but also one batch of Dutas from United when I couldn't be arsed to sort out a shipment of Avodart from merlonipharma.ch