ive owned lots and lots and lots of cars over my many years of driving, and ive owned/ driven almost every engined almera and 306,
i personally would avoid the smaller engined 306's the ones i mean are the 1.4/1.6 TU 8v engines, as they are gettin on abit now and arnt the best in the reliability league, but as a whole the 306's are fantastic cars and by far one of the best model's peugeot have ever produced, the almera is also a great car, although less desirable to the masses like the 306 hense you can get alot more for your money with an almera vs 306, spares will be more expenisive on the almera but the 306 will break more so i would have thought servicing costs would equal them selves out but the 306 will spend more time in the garage than the almera will
so yes the nissans rust alittle, but thats easily sorted if well looked after. 306's how ever only rust due to accident damage repairs so be carefull if you do find rust on a 306! it will be hiding something! and the smaller nissan engines are more reliable than the french offerings and really willing and feel sporty where as the 1.4/1.6 engines you will find in the base model 306's are sluggish and noisey. also the interiour on a french car will try and fall off its clips at any givern oppertunity and all though the interior in the almera is alittle boring in comparison, its very well made and will last the test of time. and depending on age i think you will most probably get air con in the almera which will genrally work! but ive persoanlly never seen or owned a 306 where the air con has actually worked lol!
so in summery:
306 is a good car but only worth buying the gti6/meridian models as they are well equiped or the brilliant d turbo engine, but all of these models are out of your £700 pound price range.
the almera will be strong well built and fun to drive, spares will be more, but much more reliable and i believe it would be a great first car
good luck with your car search
steve