If tea tree is not the only oil that you use and if you need a lot...I think getting it from the States thru internet is the best.
Below is the the site that I have been buying my essential oil, costs are amaizingly cheap althought shipment will sometime cost more that total amount of the order, still very attractive bargain.
www.camdengrey.com
You can also find lots and lots useful info on essential oil and related products from this site.
It is really expensive to obtain from the local market, I bought the packing of 10ml from BODY SHOP, it costs about $50 for the mixed one, I mean added with alchol and water, it is not worthy buying there, but the price is much higher to get the pure from other shop.
By the way, would Charlie please send me the method of making athletic foot mixture while you are free, thanks!!!