Any independent shop worth a darn should have no problem installing either of those. The shop you went to is clueless, drop them, don't ever go back, and find a small independent shop that's been around for a while.
And Stellar does make an alarm that is a breeze to install, but your Prestige by Audiovox alarm isn't that bad. You almost never hear me say Audiovox isn't that bad, as most of their products suck, but their alarms are ok. I sell them, my roomate and both of my installers have one and they work well. I'm actually gonna put one on my car at some point.