Hey mate,
It pays to shop around and not compromise at all it will end up costing you more, its better to spend a few extra thousand on a car than spend more later on a car you bought cheaper in order to get it up to scratch. Although having said that it is possible to find a good quality GTR for less than $20,000 as i did, but it took me a few mths of waiting. Im in the car industry and from what ive seen alot of the import cars all had dodgy k's, i remember 5 cars at one dealership that amazingly all had even k's eg, 35,000, 61,000, 72,000 etc. Im not saying this is everywhere, but keep in mind that more often than not the k's arent legit and are generally wound back in Japan before arrival here anyway.
As far as running costs yes they are high, but that goes hand in hand with what quality car you purchase in the first place, i did alot of preventative maintenance to begin with, which wasnt cheap but if you weigh up the cost of say a $500 fuel pump to an engine rebuild $6000 approx, its obviously the cheapest $500 you will spend.
Things i replaced or upgraded were for example, fuel pump / filter, quality plugs / coils, all the belts, including timing belt, quality oil etc. All the basic things.
Also this is all going to come down to what level of mods the car has allready, so it may be possible to save money on the above anyway, and whatever you do shop around for parts, now im guessing this is going to ruffle a few feathers, but the aftermarket parts scene for turbo cars in australia is absolutely pathetic the inflated prices compared to the same product from overseas is a complete JOKE !!! how most retailers can justify a more than 100 % mark up considering they buy most parts in bulk at discounted rates and still charge insane prices is nothing short of robbery.
Good luck.