I'm really keen to buy a Kombi (or maybe a beetle but would prefer a Kombi).

I'm after one that is running and registered but not necessarily a restored one, just a daily runner. What should I be looking for, where does the rust hide and what stuff should I be looking for?

Also what sort of budget do you think I should be expecting to have to outlay for a reasonably good one? A bit of an ambiguous question, but they seem to go for anywhere from a couple of grand for a running one that needs restoring up to 6-7k for what looks like a complete rustbucket. If I want a good runner that doesn't need much, where am I looking price wise?

10-15k for a roadworthy Bay kombi, 20 - 30 for a roadworthy Splitty. Get on Kombi Club and ask questions, there's a whole list of stickys that will answer your questions.

The other thing to do is get yourself a book.
'How to restore you Volkswagen Bus'.
Costs about $30-40 through Amazon. But it could save you thousands. Even if you don;t want to restore a bus it will show you what metal rusts on them. There is also a very good buying guide that shows you the pitfalls like little tell tale signs that there has been dodgy repairs and the like.

And as Dak said. The Kombi Club has some very good stickies. Two in particular will suit you, kombi price guide (this is a few years old so add 10-25% as they are more popular now). And the Buyers checklist.
http://forums.kombiclub.com/showthread.php?20629-Kombi-Prices 
http://forums.kombiclub.com/showthread.php?1292-check-list-when-buying-print-...
And some others
http://forums.kombiclub.com/showthread.php?30791-So-you-want-to-buy-a-Kombi%E...
http://forums.kombiclub.com/showthread.php?6605-restoration-costs-of-Splitty-...

And most of all, take your time. Definately view inside, outside, underneath, drive it, listen too it, take someone along etc, etc.... Cause there is a lot of crap out there that sells.

So how reliable are automatic kombis? Are they hard to get parts/service for? Or are manual ones better?

Also if given the choice, are the 1800-2 litre ones better than the 1600 engined ones? Or does it come down to personal preference? I take it a 1600 can be modified for performance a lot easier than the flat motors? Do they still perform capably ie sit on 100 on the highway?

Not too sure about the reliability of auto boxes. I would think if they are in decent knick and you keep them serviced you should be okay.
As far as parts, I occationally see auto boxes offered for sale, but i would think from what I have seen it would be a ratio of 20/30:1 of manual:auto for sale.
If you can drive stick then manual is easy as pie in these.

2ltr motors are exspensive to do things with from what I have heard. 1600 tp(twin ports) are a dime a dozen and easy to modify. Not sure about 1800's personally.
I currently have a 1600 base with a 1776 head setup in my bus. It will do freeway speeds. On a cold night when I got it it sat at 110 not probs for 10 hours. (less 5 hills that sent it down to 65/70/85/85/85). So not bad.
On a hot day I would probably run at 100km if doing a coast run.

Grab that book I mentioned. If goes through some things to check mechanically. Like grabing the lower pulley that holds the fan belt on and pulling it back and forward. If there is no play that is a good sign, if it moves 5mm count on rebuilding the engine in a few months to a year.

type 4's are great engiines to really punishas cases are aluminium and everything is overengineered compared to a stock 1600 , look what wayne penrose does with his ones , there's plenty of performance gear for them but it is expensive compared to a t1 based engine , and if u have $$ near 3ltr capicity is possible , but it depends what you want out of an engine ie camper , or empty panel

I guess what I want is a good reliable daily driver in the first instance. I'm not new to VW's or kombis, my first car was a 65 beetle and dad had a 76 2 litre kombi, I've had 2 myself as well, one manual 2l and an auto 2l camper (the auto was bought to donate motor to the other many years ago when this was a viable option, then sold them both) so as far as giving them the once over, I'm a common sense level headed sort of person, not one to buy based on emotions.

I don't mind one that I can tidy up bit by bit but can't see how one with rust, no headlining and not at all pretty can sell for 10k. Maybe for a splitty but not a bay. I know they are a bit of a holy grail but c'mon, seriously.

I am on a bit of a timeframe since my current car runs out of rego at the end of october and I'd rather not pay another $800 rego. The hard thing is deciding what to get - I could get a really awesome beetle for the same money as an average to reasonable kombi. While I like the idea of space I also like the idea of not having to do ongoing restorative work, but on the same token don't want to buy someone else's dodgy fix ups.

Does anyone have some figures or stats on relative fuel consumption between a beetle and kombi and any comparison between a 1600 and a 2 litre kombi motor?

maybe check ebay/carsales, you ll pretty quickly get an idea of whats for sale and what sort of money is being asked i spose. then weigh up what u get bang for buck wise, bug v bus. would of thought a bug is always gunna do better fuel economy wise(assuming engine size is the same) simply because of the aerodynamics of each vehicle. only my thoughts.

It seems these days a reliable daily driver bus is getting up around $6000-10,000. Still a second hand vehicle, so anything can happen.

A Beetle is a more common vehicle, and good reliable daily drivers are still out there for $3000-5000

one thing to look out 4 is R U S T