Ted,
There are certainly costs involved in being a realtor. The biggest initial cost for me was simply the cost associated with getting licensed actively. Online classes, license fees, etc. The biggest recurring cost is MLS and Realtor association dues. I am sure it varies wildly by city and state but in my city, you cant be a member of MLS and not be a member or the Association of Realtors. Quarterly dues for both run around $250 bucks.
Again this will vary by state so check with your real estate commission for Wisconsin. In Alabama, to have an active license, it must be held with a brokerage. By doing this, you incure brokerage fees. These can range from very little to very high. It is usually in line with the commission split with your broker. For example, a 90/10 split with a broker would cost you very high monthly fees and only top producers would go this route. A 65/35 split and I know brokerages that charge $80 bucks a month in office fees to hold your license.
For new agents that don't plan to do a lot of business, the Keller Williams franchises are very friendly in terms of monthly outlay in my opinion. You are on a cap rate and you pay very low monthly fees. This model is appealing to part time agents.
If you plan to do any investing at all and you are an agent, you can either negotiate out of the price your commission, if your broker approves or you can simply take a commission. This is assuming your brokers E&O insurance will allow you to represent yourself. Usually it just has to say in the contract that you are a licensed agent purchasing for yourself.
I would say to be a fully active licensed real estate agent, you are going to spend on average about $2500 per year just to be licensed.
Hope that helps.