I’m looking for a basic MTB specific tool kit that I can add to when funds allow but with so many brands and price differences I’m not sure what good value for money.

Any recommendations what to get and where to buy?

I would go for something this.
But it really depends on what you want to do. You may want a torque wrench as well if you are unsure on how tight is 5nm/40nm. A workshop stand and seat would probably save a lot of back ache too. Or you could just turn it upside down. 😉

Whatever you get you will still say “bollox I don’t have that tool that I need right now”, at least that used to happen with me.

Get something cheapish and replace if/when they break with higher quality tools.

Park……
Start with the
4/5/6mm allen Keys T-handle
Torx For rotors T Handle
BB Tool
Chain Whip
Cassette Removal

or Just get this one