They don't appear second-hand very often and you'll probably be
looking at $500 or more for those that do.

I bought mine from e-bay about four years ago for $750. It is Chinese
made but of good quality and robust. It has withstood very high winds
and heavy rain on many occasions, I have spent, perhaps, 100 or more
nights in it.

This one, at $600, looks identical to mine:

http://www.ebay.com.au/itm/BRAND-NEW-ROOF-TOP-TENT-3-1M-X-1-4M-RIPSTOP-CANVAS-INCLUDING-ANNEX-/263082576221?hash=item3d40f1895d:g:PpkAAOSwd3dZZE4Z

But with Chinese products one never knows which factory it came from.

Darche make a quality Australian one but it's around $1700.

ARB and the like sell RTTs for significant cost but I understand they
are similar/identical to my Chinese $750 one.

They are easy to erect but harder to take down. A small set of steps
is well worthwhile for the take-down. *NEVER EVER* force the zips; if
they won't close then you have done something wrong.

They are not much fun when you need a pee at 3am.

Be very, very careful when coming down the ladder half asleep at 3am,
if you slip the result will be very bad.

On mine, water pools on the canvas above the ladder - I'm told it
doesn't on the Darche. It's not a big issue.

You cannot leave bedding in them unless it's thin, you won't be able
to leave pillows.

Don't buy the tent thing they sell for the ladder area - much more
trouble than it's worth. Using a piece of 6mm dowel wrap a tarp
around it and slide it into the channel the tent thing would have
used then either peg it directly to the ground or run it horizontal
with a couple of tent poles to make a tarp shelter.

The supplied foam mattress soon compacts - an eggshell thingie from
Target/BigW etc helps.

They weigh about 50kg so ensure both your roof rack and vehicle can
carry this weight when driving - shock loads.

When static with you inside it will be carrying about 140kg (your
weight will vary to mine) - again ensure both rack and roof are up to
this. Also keep in mind that as you crawl about in the tent it is
quite common to have all your 90kg weight via your knees over just
one of the four roof rack supports - that single support may not like
that. I would be reluctant to put two people in a RTT especially if
they were *really* good friends :)

You do notice an extra 50kg load well above the centre of gravity
especially when serious 4WDing. Also overhanging tree branches can
cause expensive damage.

Packing up wet is a pain in the bottom. Before you need to so do
visit Bunnings and buy a plastic sheet used to cover floors when
painting walls/ceilings, about $3. Keep this in the RTT and if you
have to pack up wet spread it over all bedding mattress area before
collapsing the tent. Re-erect the tent ASAP to dry it.

Once the tent is up the vehicle is unusable so better hope there is
enough firewood locally.

RTTs have good and bad points but, mainly, I prefer mine to a ground
tent.

Think I'd be looking at a basic Camper trlr.

Starters on them are fair prices. OR buy a 7x5 trailer,
and fit one of the Tents yourself.

Buy second hand?.

Flog the Mazda and buy a zip door camper.

Believe me.
No Matter HOW confident you are.

IF you don't look after your back for a good while AFTER surgery.

You'll F--k it up and take yrs to fix. Or not at all.

I'm 75. Seen a few successful repairs, and some like you.
Still struggling after yrs.

GIVE it time. or you will be sorry.

I'm an EX runner. now.

Raced those 6 man OUTRIGGER canoes till 68 yrs old.

Then started tearing shoulder and stomach ligaments.

It DOES catch up. and I was covered in muscles believe me.

after not looking after my Flat.. feet, the last 20 yrs.
I'm in process of wearing these foot stabilisers.
FOR THE REST ON MY LIFE.

She's right. I'm tough. Never happen to me.
YEA.....

Be sensible mate. It DOES..