An example based on local pricing shows that a combined cost of a combination of possibly the best performing intake, header and exhaust for the S2000 tuned with a Hondata Flashpro may cost upwards of 7500 SGD. This would likely yield gains of around 40hp at best which seems pretty low on the bang to buck scale compared to similar but lower cost setups on the K series VTEC engines. If we, however, look at the absolute power to displacement ratio post modifications, we can see that approximately 280 bhp for a 2.2 litre gives us 127 bhp/litre which is in itself already a high level of tuning for a naturally aspirated engine.
Going further than 280-290 bhp naturally aspirated would require significant work on the engine and consequently cost a fair amount. Estimated costs for an engine rebuild up to a 2.4 litre setup, individual throttle body intake, standalone ECU and required engine headwork would probably exceed 20,000 SGD. To go to these levels of performance at this cost will require a huge commitment on the part of the owner and at this stage, it is probably relevant to consider your long term goals versus the budget allotted for the car's running or upgrades.
In my case, I have decided that the current level of 280-290bhp would be sufficient to run longer term and reliably on the track as I retain stock compression ratios and most of my modifications are simply bolted on with a tune. Although I will not have performance numbers like 12.X quarter miles numbers to boast, my personal view is that the strength of the S2000 has never been in its engine power but rather in the handling potential of the chassis thus spending should correspondingly focus on highlighting its strength in that area.