WoW Token Graph Charts
Currently the low looks to be 20272 gold, (for US servers), so if you can snag around that price you have a good deal. It does look like the short term trend is towards the upside, bringing it above 21k or 22k. If you have the time to monitor, it might not be too bad an idea to shave a few 1000 gold due to its rhythmic tick tock, although there is probably no need to pick 100g pennies in front of a bulldozer!
(You can also sort of work out an inverse market price and compare it to the black market wow gold price, note that this wow gold is across all servers so I suppose there may be some room for arbitrage serverswide that will slowly converge)
One good side you can use to keep track of wow token prices while you are away from a wow computer is
Alternatively you can also follow their twitter account