It varies by lodge and jurisdiction.
In my Lodge (North Carolina, USA) the initiation was about $100 and annual dues are about $100.
Other lodges in the area vary slightly, each lodge dictates how much they require. The money goes towards the facilities themselves, purchase of items needed for your degrees, money to Grand Lodge, etc.
Our lodge has fellowship dinner once per month and the typical donation contributed to cover the expense is around $6 per meal. We also conduct fundraisers for our sponsored charities and to assist in operational costs of the lodge itself.
There are other expenses that are borne by the individual, but are voluntary. For instance, I am an officer in our lodge, and our installation ceremony is in formal attire so I got a tuxedo. I also have a Master Mason's ring, which I purchased myself (some may get heriloom pieces handed down from family members). Many buy shirts or special clothing (shirts, hats, etc.) or items (rings, lapel pins, etc.) denoting their membership.
Charitable contributions are entirely up to you.
I try to give generously to our 2 sponsored causes (Whitestone Retirement Home (Masonic/Eastern Star community [http://www.meshhome.org/]), and Masonic Home for Children in Oxford [http://www.mhc-oxford.org/]).
During the course of time, it becomes necessary to consider our brethren and their families that may need our help - we contribute to their relief (on an individual basis) as much as we can.
There are also other appendant and concordant bodies in Freemasonry (e.g. Shrine, York Rite, Scottish Rite, etc.), each with their own dues, fees, and charitable initiatives you may become interested in joining, but they are entirely voluntary.
I imagine the amounts will vary for you, but the basic structure is likely similar (1x initiation, annual dues). The best course of action is to inquire at the local lodge you plan to petition. They will be very up front with you about it - they definately do not want the financial requirements to be burdensome to you.