I think you might be better off buying a small (2ft?) tree and battery lights separately, a lot of prelit are mains powered if ones on Amazon are anything to go by. Battery lights are easily available now at lots of places, JL, Wilkinson etc. We have a string of JL 20 battery bright white LEDS along our decorated for Christmas dining table, wound among a gold twiggy berry type garland and on a gold runner. It looks really good and is safe if the cat jumps on the table!
Would DS like to choose a small tree for himself do you think? You could make an occasion of it (when you have sourced ones in your price range.) Garden centres are quite good for decent quality stuff, and I'm sure Hobbycraft had little trees last year but you might have to wait until all the Hallowe'en stuff gets removed.