Yeah, did my own as well.  Certainly not a 'learner' vehicle.  I didn't have
to go underneath for any of mine, but I have skinny arms.  ;)  Mine ran like
a top at 108K miles until some bozo in an Astro (hate those durn-ugly vans)
t-boned it.  It was most uncomfortable.

G

is there any way i can do it myself with a book

I have owned a '91 Aerostar and currently own a '93 Aerostar and a '96
Aerostar. Between the three vehicles I have put on about 700K miles and
the '93 and '96 are still going strong.
First off, if you've never replaced spark plugs on anything, the
Aerostar is not a vehicle to learn on. I've seen a dealership tech take
four hours to replace the plugs and wires and simply give up. $600 is
too high, but it all depends on what they are going to do to it.
As far as spark plugs on this vehicle, I only recommend Autolite or
Motorcraft double platinum. If I had to recommend one brand of plug
wire, it would have to be Motorcraft. Do NOT put cheap plug wires on
this vehicle. You will regret it within 5K miles. The A4LD tranny on
this vehicle will last a long time if it is serviced regularly. If you
forget about the tranny you will regret it later.
My procedure for replacing the plugs: The left side can be gotten from
the front. The two front right side plugs are accessible by taking the
tire off. The back right plug you get from underneath. The proper
sockets, extensions and ratchets are a necessity. YMMV.

my problem is that on some days my van wont start so im thinking
distributor cap. now i took it to a repair shop and they said that was the
problem and also i need a tune up and wires and they quoted me $600.00 to
put new wires and new cap and air filter and fuel filter so my question is
$600.00 to much to pay?.and is there any way i can do it myself with a book
or anything else. by the way i am a woman could that be why the price is so
high. please help.