As a rough guide 100 lbs of ripe pears will yield approximately 5 gallons of juice. You will need to extract this juice using either a juicer (you will need to feed your pears into it by hand which can get pretty tedious) or a fruit press (which aren't cheap but if you have bumper crops of fruit for fermentation may pay for itself). Obviously you'll also need a container that will hold the juice. You then need to add yeast, campden tablets, pectolase and some yeast nutrient all of which can be picked up at your local home-brew store or at a big Boots. Then you need to find some advice on gravity and strength in perry and how long to let it brew. You'll then need to bottle it and wait while some malo-lactic fermentation takes place to add the requisite sweetness. I have made cider before but never perry so it may be worth searching the internet for suggestions or buying a good book on home brewing. I would advise you of one thing: the equipment you will need and the time you will dedicate will cost more than bought perry ever will unless you do it every year for which you need a regular supply of fruit, like an orchard.
And if that hasn't put you off, happy brewing.