Some alarm companies seem to make most of their money off service calls - I have seen alarm systems installed by alarm subscription companies for $10,000 that would have cost around $1000-2000 from a alarm/security/safe company.
Not clear if the $175 included the battery - if not, I would have expected (assuming this was not off-hours or weekend) more in the $75-100 range service call charge for this - plus probably $50-75 for the battery including markup, so $125-175 total charge. Not that much less than you paid, and in the upper range of the ballpark (higher cost area maybe ?) if it did include the battery.
Check out your manual on how to change the battery without setting off the alarm - but generally VERY easy to do yourself - just a couple of twist nut connections or clamps or slip-on connectors (these probably most common) to be removed and replaced - you just have to be sure to turn the system off first so you don't risk frying it, and of course the connections have to go on the right post, though some are idiot-proof - assymetric connector so you can't plug it in wrong way. Of course, this is something you should only have to do every 5-10 years.
