2006 Ford Explorer with 196,000 miles.
Mostly highway miles. I bought it new.

Would like to do some traveling in it this summer and want it to be reliable.
Took it to a mechanic I trust and was told it needs a complete front brake job, some front strut(?) work, and the fuel rail sensor must be replaced. 

He is quoting $1300.00 for everything. The diagnostics he did shows all other important elements are okay...engine, transmission, rear brakes, fluids, belts, hoses, etc.

The vehicle is worth no more than $3500.00 according to various online sources. I am not versed in car repair, nor am I equipped to do any of the work myself....

Does investing this amount seem reasonable, or am I getting to the point where I'm looking at a money pit?

Thanks.

If you just watched a few Youtube videos you could probably handle the front brakes and fuel pressure sensor yourself.  Under $200 in parts(pads, rotors and sensor), and a couple hours or so of your time.  What is the front end work that needs to be done?

EDIT: Even if it needs both front struts replaced you're only looking at about $400 in parts for everything you mentioned(front brakes including rotors, fuel pressure sensor and 2 complete front strut assemblies). A few hours working on it could save you about $900 in labor.

front struts are also a youtube video and some rental tools away from fixing as well.
try the hometown forum and post for some help.
even with some expensive struts you should be able to do the work yourself for less than half what was quoted and maybe a case of beer for who eve comes by to show you how it is done.

even at the 1300 mark, it isn't a money pit yet as long as everything else is in good shape on it.

I would also consider getting a second opinion.

Beats monthly car payments!

I got an old Ranger with 220 K miles ...  every couple years I have to throw some money at it.  See above.

Check the tie rods as well, those wear and you get wandering steering and cupped tires. 

That is reasonable price.

$1300 for all that....that's a good deal.

You wont get a better vehicle for $4000, so you might as well fix it up and drive it all the way into the ground.  Heck even if you only get another year or two out of it, it's worth it. 

Thanks, for the replies.  Invested the $1300.00.  Now, there is a new wrinkle.  When the mechanic dropped the oil pan to replace the gasket, he found a couple plastic pieces from one off the cassettes holding the timing chain in place....I'm told there's no way to guess if/ when that will be an issue; but replacing the chain will exceed the value of the SUV.......When it rains, it pours.

Sometimes you just have to ignore the "exceeds the cost of bla,bla,bla.."   Does it exceed the cost of a replacement that you know inside and out?  Years ago I was told I was a fool for dropping a new GM crate engine into an Oldsmobile Silhouette with 100,000 miles on it.  Dropped around $4000 or $5000 into it, cannot remember now.  But got another 175,000 miles and 10 years out of it.  When I sold it, it was still running as strong as the day the new engine went in.

it from the timing chain guide. It happens. The plastic gets brittle and can break.
They don't even show up in engines till the mid 90's. So it isn't a critical piece.  
I would drive and not worry about it for a while.

Though again, this is one of those where it can be done by a shade tree mechanic pretty easilly. Just takes a long time getting the front end off the motor to get to it.
So you pay for all the labor.

If the engine eats itself, a junkyard motor would be the way to go next, but wait till it happens.

I would not invest over $2000 into an explorer like that unless it was owned by someone who was mechanic minded. No offense but if you don't know your car needs brakes, you aren't keeping it in good condition which means there are maintance bombs all over that thing waiting to drop and I'm kinda shocked you've gotten the mileage out if that you have.

So, explorer no, F150 yes