$356 is a very good price for all that fully functional equipment that no-one will install for you; It must be like getting the latest cell phone in an area with absolutely zero cell phone coverage.
I'm sure the $356 that they won't let you spend will soon start to creep up when you start adding more wireless sensors (at approx $100 per piece) to the basic system of 2 door/window sensors plus a single motion detector.
An alarm system does NOT prevent theft. Not even when you pay the $30-$40 per month for one of the big monitoring companies.
You might like to take a hard look into what you are trying to achieve and then speak to a security professional who will be able to give you options and choices based on what you require.
If your goal is "to keep the bad guys out" then you need to look at keeping them out. With just a DIY interior alarm system you are relying on being alerted AFTER they get in.
As you say, it only takes about 60 seconds to remove your big screen TV, blu-ray player, computer and a stack of cash that you left conveniently on the side table. Most monitored alarm systems will take longer than that to detect an unauthorized entry, take control of the phone line and dial out to report the problem. Then the operator at the end of the phone will need to verify that it's not a false alarm before making the call to your nearest police dispatch location. Minimum response time to an alarm around my area is reckoned to be in the region of 5 to 7 minutes IF the break-in occurs within 100 feet of the nearest police officer on duty.
I wish you the best of luck in working out what you need and how to reach that aim
