Here's a good start:
italiancitizenship.freeforums.org/modello-ae-english-instructions-t7725.html
In theory it's quite straightforward. However there is a thing about where your home commune is, and whether it's registered with the AIRE service which operates out of Italian consulates.
www.conslondra.esteri.it/Consolato_Londra/en/i_servizi/per_i_cittadini/anagrafe/come-iscriversi-aire.html
If you are registered via AIRE, then it should be straightforward, as your birth details are already available.
In my case, my DFs decision to register my birth in 1966 ("If you think I am ever going to trust the English, then I'm no father" was how he explained to me) made everything incredibly easy. When I enquired via AIRE, I was told I was registered, so to get a passport was fill a form and submit at the consulate. My passport arrived 6 days later (beating the UK one which I posted for renewal leaving the consulate !).
Oh, yes - you'll need any other passports you hold.
Personally I wouldn't pay anyone. I'd suspect a bit like those scam sites which charge you for sending off a UK passport form.
Having got my passport, it's now my ID of choice. It's also nice to start getting job offers that wouldn't have been available if I only had my UK passport. Which is not how I wanted it, but if that's how it has to be.
I hope this helps. This is a NC account, but I will see updates.
In the meantime, I'm restarting the journey, as now I have got my passport I want to get one for my wife de jure matrimonii. And then my stepson de jure sanguinis
In bocca al lupo !