SMBLA. You need to do the 2-day TCL training, consolidate with logged rides and then do the TCL assesment. That lets you take people on rides up to say a 'red' level within 30 mins walk of help and at less than 600m's altitude. Or something like that.
I think that I paid about £180 for the course and £120 for the assesment.
Then you need a 2day 1st aid course. I think that was £180.
If you want to go on to MBL it's basically the same as TCL once more.
You'll need to factor in kit unless you can borrow some. Group shelters etc etc…
You can't go wrong with Jules at Cyclewild Scotland for your courses. Based in Aviemore you'll end up doing some fantastic riding and getting shown some little known treasures as well as getting your qualification.
For first aid I used Glenmore Lodge and did the BASP one. Again top quality.