Many thanks for all the replies - all interesting, and all helpful (even those who think it wouldn't work for them, or at all, because of the reasons they give). I'm most grateful.
Someone asked where I'm coming from - we're a fairly small club with the benefits that we're a friendly bunch and, more important, there's never a queue to get a launch (though you might be queueing for a particular club aircraft if you're not prepared to fly whatever is available right now). I reckon we could accommodate 10-15 new members without ruining this. And of course, more members = either lower costs all round or money to spend on new toys.
I've noticed that there have been a number of recent threads on gliding here, so I reckoned there might be enough interest to make it worth putting a package together. And I know that PPLs like flying!
The fixed price to solo model is because I know that PPLs are used to thinking about cost in terms of £X per hour. Because of the uncertainties about soaring conditions I can't do an hourly pricing model - pricing is launch cost + £Y per minute in club aircraft. Thus some aspects of training can seem ludicrously expensive in hourly terms - for example a 1 minute flight learning how to cope with cable breaks. So the theory is, offer a fixed package which at least enables the PPL to get some idea about whether it's decent value overall. We have PPL and ATPL members and thus some idea about how long, on average, it takes to reach solo - and, as you'd expect, the quick learners balance out the slow ones. Plus we're looking long term - even if you take a long time to solo, if you stay a member and carry on gliding that fits in with our long-term aims.
Once you're solo, the cost of gliding becomes fairly predictable ifyou learn to soar. I fly about 50 hours a year for between £2k and £2.5k all in, which includes all the running costs of owning my own aircraft. If I shared it with one other pilot I could cut that to between £1.5k and £2k, but I'd probably do only 40hrs because I wouldn't be guaranteed unrestricted use of an aircraft every day I was able to fly and conditions were good. In our club aircraft you can fly 20-30 hrs a year for around £1.5k - hard to do more because you have to share the aircraft on the good days and small clubs like mine only operate 3 days per week.
I'd be particularly interested in further comments from those who might be tempted, if their local club offered a package, to know what they'd want to be told, what would help attract them and what things would put them off.
Some things I can't change, like the amount of time involved. Training has to be half-days minimum, because of all the uncertainties involved, and anyone who takes up gliding seriously will find it's done in full days. A typical gliding day for me might be 40 mins assembling my aircraft, the same helping others to rig, an hour or two doing club stuff while I wait for the weather to come right, 2-6 hrs airborne, an hour derigging and helping others, plus of course all the time spent chatting with friends about our flights. Now I've written it out I'm slightly surprised that it only takes one day!