Are you saying it is $500 for a P28 ECU WITH Hondata already installed? If it is just $500 for the ECU, then that is too much. I bought a P72 ECU for $100 bucks which can be socketted and have the s300 chipped into it. I suggest you get S300 btw.
Yes you can use P72,P30 or P28 which is basically ANY OBD1 ECU with VTEC and is 5 speed manual. You wll also need a OBD2a to OBD1 conversion harness.
If you are conifdent with socketing and have the necessary tools, then go for it.
As for tuning, this link has a list of tuners:
Hope this helps.