The repair estimate seems high to me, all timing chains and related should book around 18 hours labor, suppose around $150/hour is $2700 labor so your initial impression it should be $3K total is right paying a premium for labor, while many mechanics would charge less than $150/hr.
I would look around longer for a better quote, but first I would want to see the underside of the vehicle because Baltimore gets some snow and with salted roads, could have some rust damage under it which would be my biggest deterrent.
Yes other fluids and minor things are assumed to be needed as well but such is the case with any older vehicle. People who take the best care tend to hold onto them and want a premium when sold... as they rightly should, because book value on a vehicle can't differentiate things like this.
Normally the tranny lasts more than 91K mi with no maintenance on it yet, and not in a particularly hot climate, so I suspect they drove it hard, maybe towing.
Whether it's worth it compared to other examples in your area at $5K, depends on their condition and specific mileage. They too, could be not too far off from needing timing chain or transmission work. That's just how it goes when an SUV gets to that age and price point.
If you only looked for repair quotes at major shops IN Baltimore, then I'd look further out of the city, rates should go down. I'd also look at independent mechanics for a labor rate at $100/hr or lower, but would want to see a lot of good references that they get work done in a timely manner. Maybe it'll take a few weeks but you don't want it sitting around for months which can often be the case. I'd draw up a contract for an independent with "time is of the essence" and a completion date in it, and not pay much up front. At the same time the mechanic doesn't want the value of their time tied up without payment assurance so you can either set up an escrow for payment or make scheduled payments based on reaching each stage of repair completion. It would be nice to also have a warranty, with terms appropriate to the cost of the repair... more so if paying $150/hr labor than $50, for example.