I'm sure you'll find out but "typical" prices can vary hugely!
For a lesson, depending upon the level of the instructor, whether you have a private, semi-private or group or 1/2 hour, 45 minutes or an hour you can expect to pay anything from £20 ish to £50 plus.
I would imagine, that hiring a horse would be pretty difficult - but many RS offer part loan/share of their RS horses. Or, after lessons you could look to part loan or share privately, again prices for this will vary but you could expect to pay between £20-£60 a week for a share scheme, plus possibly some extras.
I'm sure you already know this, but I'd always reccomend that people take lessons at a British Horse Society (BHS) or Association of British Riding Schools (ABRS) approved yard. Details for riding schools in your area should be on their websites
Good luck, I hope you enjoy riding again!