I had Lancashire U14 trials for the 08/09 season. You can't just turn up you are invited, either put forward by your school or club. However, to be honest, they were a waste of time and badly organized. By date was changed several times, and when I finally did go it had been changed to an hour later, due to a kids party taking priority. I wasn't even informed of the change. Then when there and the trials began none of the coaches knew what size ball to use (I.e. Full size or not).
The first lot of trials (there a 2 to begin with, I only turned up to 1 however as I wasn't impressed) were indoors. These were around October (Can't really remember as they were changed so much) and were in the indoor nets at Old Trafford. This was another mistake, having the trials out of the playing season and in the winter when no-one had been playing cricket. If you have impressed the coaches then there is another trial which are outdoors around April and May, which you must get through to get to the final trial, which then decides who will be in the squad.
5 people from my school (including me) had trials, 3 didn't turn up at all, I went to 1 out of 2, and the other guy went and got to the final trial (waiting to find out whether or not he is in the squad.) 1 of the 3 (excluding me) that didn't turn up was ex-Lancashire, and he himself didn't like it. 1 was injured and the other 1 didn't turn up as he had heard how bad it was.
The actually coaching/playing games I think is free, however you must fork out a few hundred pounds to buy the official suit, etc.
EDIT: Also I don't think district has anything to do with it. I played district, however district is kinda 'half-baked' because several of the best players from most districts just don't get in for some reason. This is normally most of the best players are from one club side and people feel awkward picking a district side mainly from one club team and the other is that a coach from a club team is the coach for the ditrict team and are often bias to their own club and pick players from their club who probably shouldn't be in the team.