I'm not 100% on the numbers but I know I'm close.
Stihl and Husqvarna: 50,000$+ initial investment, that includes displays, signage, parts, accessories and equipment. You have yearly sales minimums to stay a dealer atleast 30,000$ typical. You have to participate in marketing, seasonal booking programs,
Echo and Jonsered: 10,000$ initial investment You can get in the door for 10-20 pieces of whole goods, and 2,500$ in parts
Dolmar, Red Max, Kawasaki: 2,000$-5,000$ initial investment. Can be a dealer with 5-10 pieces, and a grand in parts.
To make a couple extra bucks, get yourself a chain sharpener and some grinding wheels, and do chain sharpening. Little investment or overhead and you can bring in some decent cash in your spare time.
Get an account through Oregon, Stens, Rotary, Ahlborn and set up an Ebay store selling aftermarket parts.