Usually all event items are easy to attain for low-level characters without much gil. Almost all of the time, you can do the event with a level 1 character without any gil (Azimuth Circle), or else high enough that you don't get aggro from the newbie areas and have a couple k on you at most (goldfishing event). There have only been a couple higher-level events, including one where you need to have an airship pass (this year's New Year event), but those are rare. Also, the only time you need a lot of gil is if you plan on buying items from the Moogles. Swimsuits this year went for about 50k, I think...But I'm not sure. So just hope you don't have to buy the Halloween items from Moogles this year.

As for the Halloween event, you usually need to buy sweets and snacks to give to NPCs. The prices on these things tend to soar during Halloween, so I'd grab some now.