This info isn't 100% accurate and a year or two out of date but...
ACC
Certain costs are inflexible. After finding a venue we knew that we would incur the following costs:
Food - capped at £10 per head but with flexible options that meant we actually spent a little less.
Venue - £80 cleaning fees (2 days so 2 x £40). Many "free" venues have a standard fee for cleaning. £40 isn't a bad price for a room for a day though
Running Costs - ~£15. The ACC runs an unusual format that requires ALOT of printing. We didn't budget for this but iirc it tallied nicely with the underspend on food.
At this stage we decided that £20 was a reasonable ticket price for a full weekend event with two hot meals. This figure was mostly pulled out of the air but after running the numbers it still made sense and a quick glance at other events was enough to check that we were providing decent value for money.
We (perhaps optimistically!) predicted that 20 people would attend. Hence:
£400 Budget
- £280 Inflexible spend (meals+venue)
= £120 to spend on prizes
In hindsight we should have taken a more conservative approach and spent very little on prizes. I don't regret the decision because we had fantastic prizes (well over £120's worth thanks to some judicious purchases by blocknroll). However, by limiting the amount spent on prizes we could have given ourselves a much smaller break even figure (15 players rather than 20) and a bit more leeway to screw things up, such as the unanticipated running costs. Any ticket sales pushing us over budget could have then been set aside for the next year so there was no real reason not to take the cautious path.
Advice For New Events
1) Venue - the venue is the single most important part of your tournament. No venue, no event.
The venue will dominate your planning and thus your budget as well as setting the ambiance. Find the right venue and book early.
It is never a bad idea to keep in touch with the owner/manager. Sometimes pubs go bust or lose track of who booked which weekends. If either of those things happen then you will be the last to know. Don't go mad pestering them but giving them a nudge every couple of months can help dodge a nasty surprise.
2) Value - don't go mad buying toys for your event. If you have the spare cash to buy everyone a customised-gold-plated-dice-that-is-also-a-coach-figure then by all means do so. It is probably best to keep it simple for the first year though. Focus on delivering a well priced and well run event.
3) Viable - it is important, albeit not alliterative, to make sure that the event runs smoothly. Make sure that there is time for people to finish their games. Give yourself time to process results. Plan how that is going to work (are people going to hand in their results on a sheet? etc). If the event runs smoothly then people are more likely to enjoy it, especially you.
Other things that didn't fit into the "Three V" framework:
Prizes - certificates are a nice minimum
Accommodation - write a list of local B&Bs and hotels
Parking - also, transport links (buses, trains and planes)
Food - this will depend on your venue. If you are in a pub or other food selling place then pre-ordering food can be a good way to build a good relationship with the venue because it makes it clear how much custom you are bringing them.
Format - make sure you have a rulespack, bullet points will do.