Don't worry about flies. There are several generic patterns of floating and sinking nymphs like the Hares Ear, Pheasant Tail Nymph and Daddy Long Legs that will catch anytime anywhere. You'll get by in the first trip or two with about 5-6 different patterns. More often than not I've used no more than 2-3 patterns in a day's fishing. As you progress then you'll learn about flies from experience and from what other fishermen are using on your local water. What you need to concentrate on, is making sure you have the right gear and knowing how to cast effectively and safely. Rod, reel line combinations need not cost a lot and a budget of ?100 will get you started on the water and will catch fish. Don't forget it's not only trout you should be thinking of. You can catch pike ,carp, perch, chub, roach rudd and I've caught bream in september when they are fry feeding. As a start you should buy Trout Fisherman magazine and find yourself a casting instructor, preferably based at a local trout lake and check that they can supply equipment. The mag will also have ads from the major retailers which should give you an idea of the cost involved. Airflo are a good budget supplier as are John Norris. Ask the instructor about suitable rods, reels and bitz, they are usually very helpful and will steer you clear of the rubbish. Also take a look at
www.globalflyfisher.com. It's a good site with a lot of useful information about tackle and flies. Good luck and if you are just starting out with a fly rod, the most important piece of equipment is a pair of glasses preferably polaroids. A learner and a fly rod can do a lot of damage, usually to yourself.