work on getting the common class cards for druid - druid of the claw & wrath, those should make your deck a lot better
something like this is feasible, i think
generally speaking though, druid is not a good F2P class b/c the best cards (ancient or lore/war, force of nature) are epics
if you do decide to spend money, buying naxxramas would also make the deck a lot better - belcher, zombie chow & loatheb are all great choices, and even spectral knight is pretty good