Several improvements can be made to make OPORCON competitive to commercial products. All of these will change OPORCON controls, as iButtons are proven technology, used commercially in numerous factories for time attendance, metros as e-tickets etc.
Better timing: by using an RTC in the control, much better accuracy can be achieved. Easiest way is to add 1-wire RTC like DS2417 because OPORCON already has support for 1-wire in it's program. Price of such system will put the price up a few euros, and give accuracy better than +-4 seconds per day (in the worst case without using a timing enhancement system already programmed in OPORCON).
Audio signaling: piezo speaker can add audio signaling for the price of few euros.
Programability: current OPORCON system needs per control chip pre-programming, because of timing enhancement system which is dependent on element on the control board. 16F628 used in this system can be programmed when it's on board, by using In-circuit Serial Programming. Change to the schematic can make re-programming of controls easy. This won't put price up, it's a simple rearrangement of elements and one connector.
Control ID change: as with programmability,
current OPORCON system is preprogrammed with control ID. Using a 5 position DIP switch users could choose from START, 1,2,3,... 30, FINISH controls. Price of DIP switch is a few cents.
Memory in the controls: by using a memory chip, runner cards ID could be saved locally for each visit. This way there's a backup in controls in case card fails (although, by IOF rules this doesn't mean squat). Easiest way is to use a DS1996 iButton, which can store up to 64kBit of memory. Each iButton has an ID of 48bit, so over 1300 cards could be saved. Reason to suggest DS1996 is easy recovery as no additional hardware or software is needed in OPORCON - DS1996 is another iButton which can be read in iButton adaptor. This would put the price up 10 euros.
Connector: it this version a home made iButton connector was made to be durable because original Dallas connector didn't look it can handle a lot of users and elements of time. There are 3rd party connector makers, which make durable high-quality connectors. Those are 5-10 euros.
All of these changes would make OPORCON competitive, at the fraction of cost. Normal price is 10 euros, adding timing, piezo speaker, a better connector and memory will put the price up to 30 euros - still 2-3 times cheaper than competition.