1. New tyre about 230 same brand.
2. Widely available but shops are not recommending this tyre, saying that even buying cheaper tyres will give better performance then the stock tyres. i end-up with Davanti tyre, the cheapest option available. I resist the tempatation for Falken (Thai) as the one that I used before very noisy.
3. imho you can change single damage tyre but it will create an imbalance (although in most cases its negligeable) - http://www.universal-tyres.co.uk/news/repl...two-better-one/

I only have answers to your question no. 3. I have previously replaced a single tyre on the rears to another brand. Only a slight degradation in handling in terms of sharpness in steering is detected. Though it is nothing serious as it drives fine in all driving conditions. I have just replaced a single tyre on the rear earlier last month as the tread has worn off. Coincidentally the tyre shop has the same Champiro Bax 2 tyres for sale at RM40 which looked pretty new so I took it. The rear tyres are still on different brands (one is the Champiro Bax 2 and the other one is another brand).

30,000 km / year is not exactly high. Proton's maintenance can be considered to be relatively low. It's just the major maintenance that may be costly (RM1,400+ for the 60,000 km service) presumably due to the Turbo engine. The period of maintenance is the same as the Japanese ie. 6 months or 10,000 km for full synthetic whichever comes first. Usually the 6 months period will dictate the servicing of my cars, not the mileage as the average mileage of my car is 7,000 km for 6 months. In other words, after 6 months I would have done 7,000 km on the car only.

People usually don't go for Proton mainly because of the perceived low quality when compared to Japanese cars, not the maintenance. Maintenance of Proton cars can be considered as among the lowest alongside Perodua.