Fuel pump assembly, new sender (providing it's not just a disconnected
wire or blown fuse)  If you get this Jeep, get yourself the service
book (expensive but pays back after the first repair)

marbles is usually a disintegrating cat.  I'd listen under the vehicle and
get a mechanic to give it a once-over just to be safe.

I dunno.. is it stalking you? :]

I'd find out what he wants for it then negotiate the trade-in.
All depends on the bluebook value of your trade-in.

Could be the fuse or wiring, if not then its the pump assembly
(contains the pump and sending unit) this could be expensive
($300-$400) depending on where you get the part from.
Marble sound in exhaust is normally the cat going or gone bad and it
will need replacing, hows the rest of the exhaust?

If all it needs are these two repairs I'd go for it.  That said read
the end of this message for a list of things to look for before you
buy.

I would check out the resale value of the J**P and your Saturn in a
blue book for you geographic region, some vehicles have a higher or
lower value in different markets.

at least you know the 4x4 works :)

Ok things to check...   if the J**P has running boards on it, carefully
inspect the rocker panels for rust and holes.  Either crawl under or
have the vehicle lifted on a hoist and inspect the floor pans from the
underside, you looking for rusted out sections, take a close look at
the tranny hump area and the drivers floor. (J**P uses this really good
rubber backed carpet, keeps water on the surface of the carpet but also
traps any and all moisture between the carpet and the floor) Bill has
some pics of what a bad floor looks like:).   If your able from the
underside inspect the backside of the quarter panels and look at the
underside of the rear cargo floor (difficult to do unless the vehicle
is on a hoist).

If these areas look good, then your set.  If it has running boards,
remove them after you buy it, or you'll be replacing rocker panels in a
few years.

As was mentioned have a trusted mechanic inspect the vehicle prior to
purchase.

Snow...
93 ZJ Wifey's ride
89 Chevy Wagon
93 XJ recently retired (swiss cheese syndrome)

That seems reasonable IF he repairs all of the problems you listed
first, and it passes the inspection of an independent mechanic that you
will hire, second.  Best $100 you'll ever spend.  If he says NO, walk.