>can you recommend anything for somebody who is interested in getting into fixed wing but who doesn't have any particularly large open spaces nearby?
>Bonus if there is something cheap & which can eventually carry a small AIO fpv cam/vtx module.
Hobbyzone Sport Cub S fits the bill about perfectly, especially if you're absolutely newbie-tier since it has SAFE, which offers auto-levelling just like quadcopters do. And Hobbyzone even offers an FPV combo including the VA1100 camera, so it's a safe bet that it can carry an AIO unit.
But if you're already comfortable flying multirotors line-of-sight IN ACRO MODE, then I'd recommend building a RCfactory/TwistedHobbys 3D EPP plane instead (most any of them will do). It's not your typical beginner plane, but I've taught three beginners to fly with mine. Despite being an all-out aerobatic airplane, it works for me as a trainer because it's slow, light and incredibly durable. If you dial the rates down, you still have plenty of time to think things through, which is more than can be said for the big T-28s people were often training with a few years ago. If you DO crash, it's alright, because a) it's too slow to hit too hard, b) it's made of EPP and absorbs impact like a NERF ball, and c) if you DO break it, you can usually just glue the torn foam back together with Foam-Tac and be flying again in 15 minutes.
And despite being 32" span, these airplanes are still light and slow enough to fly in confined spaces. A tennis court is big enough for basic flight, and I can even 3D mine around my living room.
And I know it can meet your last criteria, since a friend of mine stuck an AIO on his then proceeded to fly it around a parking garage (mostly for the bragging rights of having flown an airplane through a parking garage).
And unlike other trainers, this isn't the sort of airplane you'll ever get bored of. Ever. Trust me.