If you liked using the Canon AE1 Program then perhaps have a look at a Canon A1. Small (by today's SLR standards), compact, 5 modes including stopped-down AE, light, good looking, a nice clear exposure info display in the viewfinder, well-built and usually reliable. Plus they were popular, so there should be lots to choose from so finding a mint condition, fully-working one for the right money should be do-able without waiting months. They do need a battery to work, but the type they take is still made and readily available on the internet (unlike some of old film cameras that used a now obsolete mercury type battery, such as I believe the Olympus OM1) and they seem to last ages (I think I've used about 4 of them in my A1 and I've had it since 1980!), just remember to turn the little lever to the red 'L' lock position to turn everything off when not using the camera. Be careful if opening the battery compartment door, as the plastic seems to get a bit brittle and the door is spring assisted, so it opens with a spring and can bang into the lens mount box and break, so put your finger between the door and the side of the camera body to cushion it!
Whatever you buy, I'd give serious thought to buying from a reputable dealer/shop with a good guarantee (camera repairs can be expensive and even correcting what appears to be a minor fault such as a slow or intermittent shutter could cost ££s!). If considering an A1 make sure it hasn't got any signs of shutter squeak/cough, which Canon AE models can be prone to. It's often just a re-lubrication job to fix it, but to do it properly the camera has to be dismantled to a lesser or greater extent, so those with the squeak should be priced accordingly to allow for the repair bill! With most SLR cameras of that era, expect to have to replace the light seals and mirror buffer strip sooner or later, unless it's already been done.
You should be able to get a mint-ish A1 from a reputable, long-established shop for your budget of £100. Last time I looked, somewhere around £100 was about 'right' for a fully working 'Excellent+ to Mint -' condition one with 50mm FD 1.8 lens - the price of top-quality film cameras seems to have risen a bit lately (probably due to people such as yourself discovering the film side of photography?), so don't begrudge an extra £10 if it's a really nice one, chances are you'll get your money back if you look after it well and then decide to sell it. However, don't forget to haggle a bit - if you don't ask for money off you won't get it!. Lenses for future - have a look at the Canon FD 35-70 f4 zoom (the metal bodied one, not the plastic bodied replacement) and the FD 70-210. That should cover most situations. Hope this is useful, best of luck choosing, and welcome to the world of film. See you in the 'Talk Film and Conventional' section of this forum in due course!