Alice - It sounds like your pricing is excellent, especially installed. I have heard ranges of as little at $5K on up past $10K. Your quote is definitely at the better end of the spectrum.
One thing I might comment on is the resale. I don't think you will take as big a hit on a Viper modification, especially if it is done by the right tuner. Case in point: I sold a Doug Levin car that was producing roughly 900 HP. This was on an older Gen I with a pretty fair number of miles on it. Figuring the inherent value of the car itself against what it actually brought with the DLM package, and it still managed to recover roughly 75% of the upgrade cost.
Conversely, had the system been removed and the car returned to stock, the combined price of this used Viper and a take-off supercharger system would not have equaled everything sold as one. It was the Doug Levin name and installation that helped bring that price, just as it would from a number of great tuners like Heffner, Cragin (DC Performance), RSI, SVS, etc.
The bottom line is that on a Viper you will usually retain more of your investment on aftermarket goodies than you would on, say, a Mustang. Especially if that investment is with a well-respected vendor - any number of which can be found right here. For $7,000 you could have Big Earl doing the install and you will still be just fine as long as it runs well. That is a great price!
Keep us posted on what you end up doing.