Ok, firstly when you apply for mayor you are also applying for a town. (It still costs 85k) Before you apply, mark out your town (it has to be between 100x100 and 200x200) with signs. You should write the co-ordinates on the sign along with the town name on the sign. I'm not really sure if you have to do that but I do it anyway.
Town portals cost 75k. When applying make sure to make a frame of obsidian to mark where the portal I going to be.
Finally for the other benefits:
More Lwcs, ability to apply for president (more towns), access to the mayor+ section on the forums and more! :D

 

A 4x5 portal is 75k, but if you wish to have a 5x5 portal, it's 85k

 

Once you have a town, you can sell plots in it to trusted members of the server, or your friends, or ppl you like, or just random builders. This raises revenue for you, and they can build homes that will make your area look nice, and you won't have to be the one doing everything in your town. I, personally, don't see any reason to ever select less area that a 200 x 200 since there is no cost reduction between the different sizes.

You can build your own personal store front, to sell goods or services to members of your town. After you get a town portal, ppl can be directed to the entrance to goto your town to shop or use any services your town may provide. Heal signs replenish all dmg and hunger when you click on them, and are 40 K. Very helpful. You can put a heal sign next to lift signs, and have a leveler for acrobatics skill. You could put a heal sign in a pvp zone (also costs 40 K) and have a training area for ppl to level up their pvp skills.

These are all features you can add to your town to draw more ppl to your town, or to make your town a better place. Read the forrums page for "Mayors + Applications" and you'll get a more comprehensive list of all of the features you can have added to your town, for what costs. I hope all of this helped.

 

I love being a mayor lol. I don't ever plan on getting president... #Mayor4Lyfe