my friend had the viper system installed in his 400E with remote start and all the other things u mentioned, however battery backup was not part of the system. He had it installed for about $180 (labor and parts included) and the person who installed it did a really good job. The installers seemed to know what they were doing. I will get you the details from my friend as to where the shop is. I know it's somewhere close to woodbridge, NJ. It's a privately owned shop. I intitally wanted to do the job myself as well but the hours and hours of labor to save about $40 was really not worth the headache / time. The alarm system itself if bought without the installation is around $140 but DEI won't warranty their products unless installed by an authorized installation facility. So at the end I really dont see the benefit of making this a DIY unless ofcourse you don't care about the warranty, or if the product that you plan on install is not manufactured by DEI. and about 90% of the alarm systems are made by DEI.
good luck ! I will post the info once I get the name/ or number of the facility.