Keeping hens is really cheap!  The cost is time rather than money. But it is a hobby not a chore.
Once you have bought the housing and fencing materials, the feed and bedding costs are probably less than running a dog or cat.
My run is larger than most as I wanted to allow for flock expansion. Start with four birds then maybe double then triple.
Many people give each hen an area of only 2' by 4'. About as big as a bunny hutch. A bit cruel in my opinion.
Fencing 400 (agricultural supplier or DIY store)
Hut 100 (ebay)
Laying Pellets 20KG bag 5.80
Mixed Grain 25KG bag 6.20
The feed bags last my 4 hens 6 weeks, whereas Humphrey probably costs me 6 per week
Sawdust Bedding 1 bag (waste product)
Shredded Paper Free - get it from your local admin offices
The costs are inexpensive but the frequency of cleaning the hut out depends on how big it is.
I have 4 hens in an 8-hen hut, so it needs cleaning out every day.  I swap the bedding very morning.
When you clean your hut you can check for any unwelcome visitors: mites, mice, etc
Allow time for maintenance. I use clear preservative inside and wood preservative on the outside. 
You don't want it to be dark for them inside the hut.
Use a red mite powder occasionally to control this parasite.
Waste disposal
You need a reasonably sized compost heap, preferably two for rotation.  Mine are made with pallet walls.
Mixing hen droppings with shredded paper and general garden waste creates a balanced compost.
The paper is alkali and the droppings are acidic.
After a year you get a fantastic compost for growing monster vegetables.