A quick brain dump of most stuff.... bit long but useful if you are starting out
Caravan price from minimal to £40k depending on your budget, taste etc - if you have the time, you can refurbish an older van and get a bargain, or if money no object, go visit a few dealers to see what you like.
Tow car - needs to be heavy enough to tow safely - ideally van should be no more than 85% of kerbweight of the car and legally no more than 100%.... if you are buying a big heavy van, you will need a big heavy car, especially if going out in the winter season, or going rallying
Tow bar - on new cars can be upto £600, but a towbar fitter will be cheaper than a main dealer usually
insurance - varies but around £350 for new for old policy, can get discounts depending on storage, alarms, locks
Storage if you need it ranging from virtually nothing to around £400 for gold storage site (see CASSOA web site for more info)
Servicing around £100 - £150 per year
Leisure Battery (if buying new van or one without battery) between £70 and £120 for 110 amp battery if you shop around
Gas - you will need either Butane (summer season only) or propane - after about September, overnight temp can be too low to use butane. You could theoretically survive on just hook up, but it can be really unpleasant if it fails... and if you're on a site without, or rallying, its essential. Calor available most places, but local suppliers are cheaper, though you can't swap cylinders outside their area
where you will stay - Caravan club sites range from £7 per night for v basic pitch to around £30 per night for family of 4 on a super service pitch in peak season, some sites are members only - membership is around £35 for joint members - Camping club is very similar
For budget weekends and holidays, look at rallying with one of the clubs - can be as little as £10 per weekend but own sanitation needed and usually no electric hookup
breakdown/recovery - clubs both offer their own cover that is for your car and van and offers added benefit of dual recovery - if you break down on the way to your holiday, they will get you there and back so you dont miss it....
This year we will have around 5 weeks of holidays plus numerous weekends away in both Britain and France, all for less than the cost of a reasonable 2 week package holiday.....
now if only work didn't get in the way....