How do I do this without getting screwed? (aka "I always get robbed before I can get the power!")
Well, you must plan. I used to post the locations to the FTA on a fairly regular basis and usually in a very usable format, and it seems that once my absence struck, others have carried on the custom. So you can plan out, with the use of maps and information, (like that available here), the route you plan to take, and how much AP you, personally will need to get from your current location to attaining the power.
Basically, you need to see how many moves it will take for you to get from where you are, to a bank to withdraw, (the one closest to the Guild, so you minimize the amount of time which you carry your money one you, decreasing thefts) to the Guild, and at least 5 squares away. 5 squares seems to be the minimum distance one can safely sit from a known Guild and not get over-run with thieves and biters.
NEVER sit anywhere near ANY building or Guild with the money to pay for a power ON you. You will certainly get it robbed.
The best thing is to plan out the # of AP, know where you are going exactly, go to sleep and stock up more than enough AP to do what you have to and get away, hopefully leaving you in a safe area later, never having been robbed or what have you because you never stopped moving long enough to get snagged!