To start you dont alway have to have net out there. I have installed Tons of cameras in barns and metal building in 6 years of security work that didn't have net on site. The thing to think about is how the building will be sealed(Door types, windows, Etc.). Then the layout of open spaces in the barn/shop. Now all that said let me give examples for setting something up.
Now lets start with a basic square building. It will have four walls, the roof, a open floor space, one human door, a overhead door and one window. If you're just looking to just keep an eye on the building, four cameras is all that is need. They can be placed at eave height and at the corner of the building looking to the next corner. This will let the cams see the whole of the exterior of the building from camera to back of the next camera. As for an alarm, I prefer to hard wire everything. But i know that is not always do able. So that said you would put a contact on both doors. Now for the window there is three ways to cover it. one is with a contact on it, the seconded is a motion in the building, and third is with a glass break sensor.
If you plan on using a motion you will need one rated for outdoor use, unless the space will ALWAYS be conditioned. A normal motion will not work below 0 or above 110 degrees( this is just a baseline, the ones I use for home apps is -14 to 130 degree op. ranger
http://www.security.honeywell.com/h...sensor/motion/dual-tec-residential/18987.html ). That being said for what i us, they are still not good for a shop/barn that is not conditioned. I live in South Texas and a closed metal un-insulated barn/shop you can damn near cook in lol. You could use a photo beam but birds, rats, and animals can trip them causing fails alarms.
As far as the alarm goes even if you don't have a pots line running out to the property its all good. We have been using GSM's for years now(its a cell phone for your alarm). So what would that barn/shop need. I would Quota you for a 4 channel DVR, 4 fixed optics cameras, and a basic alarm with GSM.
A basic alarm in this parts would run 19.99 to 25.00 and month with a 10 to 12 dollar and month charge on top of the alarm fees. For the Cameras it depends on the type and quality of the DVR and Cameras you're looking for. A basic 4 channel DVR will be 300 to 800 dollars(most of the cost is in Storage size of the hard drive. A HD DVR will start at 900 and it only goes up.
A 420 line rez fix optics camera starts at 150 a cam, a 640 line rez vera focus camera will start at 250. A HDSDI camera starts at 450 for a fixed optics.
I could write a small novel on this lol but if you're really interested in doing something we really need to see a blue print of the building you're looking at to tell you the best way to secure it.