Joining a club is not necessary more expensive than fishing on your own, but there are some things to consider.
I see you are staying close to the sea. So you dont have the costs of an inland club that has to travel all the way to the coast and stay overnight or for a weekend
If you are a person that fishes regularly, you might as well fish the day that the club has a comp or social.
Fishing by yourself - you have the tackle - you buy the bait - you travel to the beach etc (These costs should not really differ when fishing for a club - local)
When joining you obviously have some costs -- subscription - club colors
Then after that its much like fishing on your own, you can also choose if you want to join the guys and go fish at other venues with the club. But its not a have to.
Later when you have developed to such an extend where we start talking provincial trials and teams, then it becomes expensive.
Hope this helps, maybe not explained in detail but I am sure you get the picture