Storage sheds

Without spending a lot more your not going to get much better, if you decide on the wooden style make sure its tongue and groove rather than over lap .
You can beef the security up by adding extra brackets so the roof / side panels are more secure or as i am planning chicken wire inside , if the side panels get cut then the tea leaf will have to take a while to cut each strand.
Look into a floor anchor through the floor to a concrete base or a bucket of cement with an upturned d lock to make an anchor.
The lock should be in a padlock protector to keep it from the elements and make it very hard to get a cropper on it

Hinges for the door should be security screws that cant be undone , the same for any handles/lock clasps and wall anchors if you go with them.

Dont keep tools in the shed that could be used to remove locks etc
This is interesting
http://www.bikeradar.com/gear/article/b ... t-1-21131/
I went for one of these in 7x5 and spent a while beefing it up but its more than your budget
http://www.localdiy.co.uk/Products/2426 ... tAodwVkAaQ
Originally i wanted a concrete solution but i did not have the funds so i had to make the best of it as well as security marking the bikes.