1st car I owned was a 1978 Datsun 120y sedan, nice fun rear wheel drive manual, 1.2 ltr engine. I think I payed about $1,500 with 12 months rego, and this was about 8 years ago. I kept it registered for about 2 years, and decided it was to much effort to maintain so sent it to the wreckers.
Next I had a 1981 Ford Laser. Great little run about car, but it was a write off thanx to a big 4WD ramming me off the road (seriously).
Next I had a 1985 NISSAN GAZELLE. This has been one of my favorite cars to date. I payed $800 for it as it was just out of rego and need a fuel injector replaced. This is an awsome machine, 2LTR motor rear wheel drive, 2 door, pop-up headlights, electric windows cruise control. Unfortunately I crashed this on Victoria Rd when I was cut of by a 200SX with blacked out windows.
Next I found the deal of the centry, a smick 1973 TC Cortina Wagon for $400, 2 months rego. This thin is huge and awsome. 4.1LT 6 cylender motor delivers so much power. Anyway, this car is currently at a pannel shop as I am investigating fixing the rust and touching up the paint. FYI I know the guy doing it and if I help with the prep work, it will probably be pretty cheap.
So my current vehicle is a SUZUKI VITARA 4-DOOR ESTATE WAGON. Great 4WD, 1.6lt engine manual. I only payed $5, 800 for it, but did not get it serviced for straight away and the engine & gearbox died (timing belt came off and screwed the camshaft??!). So I had to spend $3.5K on getting a new gearbox and engine put in.
I often see a Suzuki Sierra and wish I had spent half the dosh on a clean one. But all that aside, teh Vitara is great on and off road.
If for example you decide you want a Sierra, test drive atleast 2 different vehicles to compare performance. Also, if your budget is $4K, maybe only spend a maximum of $3K, to allow for extra costs.
Try this website for pricing of second hand cars, although not entirely accurate, it is a good guide -
www.redbook.com.au
Another option is to buy something cheap and practical with rego now, and just take your time to find the right car for the right price. You can always sell the car again later, or in some cases just wreck it and get into your new car!!