1999 Vauxhall Astra

my vauxhall astra the (rev counter does not work and the engine mangment is on all the time) i took to vauxhall delear they told me the (engine control unit) has to change it for new one and very expensive? any i dea can i buy second hand or i repair my one? but i been told is requier reprogramr it

what can i do to fix it do not cost me too much?

thanks for you help