1) First, you have to know which model is that zoom multiefx. As for the price, here is the sale catalog for city music year end sale. Inside contain the sale price list for zoom multi efx. Check and decide yourself whether is it worth it.
2) Decent and good overdrive prices can range from $100/$100++ to $400+ to $500+sgd. Again, it depend on individual on whats decent and good. For a start, you might like to check out the gear reviews forum. Moderator Subversion has some reviews there, that might be useful for you.