What age of BMW are we talking here? If something with an M50 or M52 engine, it'll be perfectly happy on mineral oil.
Here in Australia, there are a plethora of mineral and semi-synthetic oils that meet ACEA A3/B3 or A3/B4, which can usually had on the cheap if you wait for sales. Oils with this ACEA specification are better than "any old oil" you'll find off the shelf, particularly 5w/10w-30 oils that may be ILSAC spec. and absolutely inappropriate for a European engine. The ACEA A3/B3/B4 specification also makes provision for longer oil change intervals.
Unless you can get fully synthetic through an oil supplier in Australia, you're better off with mineral oils, unless you know you can push synthetic to the absolute limits. Some of the LL01 oils can run even more than what JFAllen suggests.
You folks bashing the O.P. "because he drives a BMW and wants to cheap out" are completely missing the point of the question. The O.P. is obviously in an area where all oils are relatively expensive, and is searching for products that will meet the car's requirements, and his price requirements.
A word to the O.P., you may find that changing mineral oils more frequently ends up costing more than a full interval on an approved LongLife-01 synthetic. Basically, a factory 10,000+ mile interval with approved oil is better than roughly half with a mineral or semi-synth.
If you had an older BMW with the 7,500 interval, I'd say a very good mineral or semi-synth would be okay (as this was the OE spec), depending on your whether short or long trips.