I've taken some photos. Hope they're clear enough.
What do you think?
Since you ask, and bearing in mind this is a dual suspension (and therefore heavy) bike - and I'm guessing rough cross terrain riding is not your primary use.
The rusty
freewheel (6sp?) and rusty
chain could be made to work. The freewheel might come off, if you're lucky skillful and strong. I'd be taking a wire brush to it and then oil will lubricate. A replacement chain is cheap (6-7sp). Need to remove the chain (by pushing out a pin) in order to get it in better nick. But then refitting with a quicklink will cost almost as much as a new chain. Procure new chain.
The
chainset looks pretty far gone. I assume it is a cheap MTB triple with rivetted rings and a 'guard' screwed on. Square taper. Any MTB chainset will do as a replacement. The bike charity list might have somewhere close to you and they'll have tens, or more.
You talk about buying a
seat for £30. How will you decide which one is comfortable, before buying?
It's certain that
all the cables, inner and outer will need replacing. Perhaps the
brake pads will be OK.
I also note the
nipples are showing rust: these are steel nipples (as opposed to brass) and mean the
spokes are galvanised (and rusting where not black).
Tyres look OK though I see a displaced
inner tube (see valve).
What do I think? I think you should
return it to its previous neglecter and go to your local tip/recycling centre where you'll find a better bike which will offer you an opportunity to learn and a far better end result.