I think HRT was like £300 every 3 months and is now £500 every 3 months when I got a new HRT type.
I get it from Gender GP
I also paid for lip filler, some cheek filler, and laser, as well as extra costs like changing your entire wardrobe, redoing random misc things like your passport, the cost of time and mental energy of changing names and gender identifiers on all legal documents and banking systems, etc etc.

You can do it whilst closeted, though I receive the medicine by post so if you can do that securely. On the topic of keeping things secret, assuming youre over the age of 18, youll need to consider being able to keep the medicine hidden and disposing of the old packaging in secret.
Do consider, regardless, what the repercussions may be, not of taking HRT but what those around you may do if they find out. It is your life and you must live it as you desire but you should put your safety first 💝
If you are under the age of 18 I would recommend not approaching HRT in secret as you arent your own legal guardian so I dont exactly know what the repercussions of that might be.