With most events being around £15, I'd pay about £15-25!
Suitable Cost to Join Event

well not really on a budget so would happily pay £ 20 - £ 30 entry fee, my choice would rather be based on location, how far away is it and do i want to travel that far too play chess, and venue, much less likely to want to play chess in a school hall than a nice venue with carpets
The vast majority of events charge £15-25 for a two-day event. If you look to charge £20, you won't be too far wrong.
ECF grading is 50p per result (2 results per game). Arbiters tend to give up their time for free. Depending on when you hold this event, and whether I have my arbiter qualifications in time... I'd be happy to run it for free if I could get to the venue. If not, it is likely that arbiters will want something, but it wouldn't be too much in excess of expenses.
As with all costs, what is a suitable cost for those that wish to participate with this event? Remember that the aim I had was that it would allow an opportunity for similar minded individuals meet and network at a chess event where all could relate.
However, this idea has evolved to include:
Although most are enthusiastic about this and each have their own plan, I would like to remind each other not to make this event too big. It would be our first year; the bigger the event, the more risk of failure.
Nonetheless, back to my original question, how much would you be willing to pay to attend this event? I would be happy to pay £25~£30 for the weekend.
Looking forward to feedback.
Regards,
Martin