That was some reading. A couple of yrs ago I too wanted to race just for fun and wanted the cheapest way in. Ignoring my first year we'll take it from this to get some perspective on how cheap you can race.
First off racing for fun just doesn't happen, no one is happy unless they are winning. If you are happy not winning then why are you out there, you'd be better off on trackdays.
The majority of club racers are normal people like you and me, occasionally a talented rider appears and wipes the floor with evreyone before climbing the ranks. So just taking the normal folk into consideration you cannot win on a standard bike. This is the first thing you find out and the first thing that demoralises you. On that grid you need at least equal equipment to stand a chance especially in the psychological game. Knowing the guy next to you has had tyre warmers on his new tyres has already made him quicker than you on your cold tyres that have done 2 meetings. Just how much do tyres/warmers cost compared to crashing your bike ? Fair enough if you don't wanna ride 100% into the first corner but it's club racing and the first corner matters in a 6 lap race.
If you're on a gris you will want to win and it's pointless trying to save money going racing.
I spent all year on a bike 15mph and 15hp down and altho I had fun it can't be described as the most enjoyable year. If I had the hp and speed yet still didn't win I could live with that as I accept I'm probably not good enough but to not know that for sure is eating away, not next year tho as the bike won't be a valid excuse anymore
So costs for a year....
entries, licence, acu, club £1000 - £1500
Bike £2000 if you're happy not winning (unless you are the next Rossi)
Fuel to the meeting, food, bike fuel, tyres £1500
Warmers, genny, spares £1000
We're already upto £6k to race a standard bike and I'm assuming sleeping in a tent ! That is just not an option at some ciruits that get bloody cold and wet. Where are you gonna stand in sideways rain, where are you gonna get dry/change tyres/repair bike in therain ?
You need to wake up in the morning fresh and warm, if not it's just another advantage given to the guy next to you on the grid
And don't forget it is addictive, I wouldn't change it for the world no matter what the cost. Just ne realistic about that cost