I'm surprised you were told as long as 2.5 years! My DS (who had bad overcrowding top and bottom) did it and it was 18 months, but only because he started literally a week before Lockdown, so he was then given a number of weeks' worth (I was regularly asked to take photos of him from lots of angles with and without the aligners) and then he just had to wear his last ones until they were able to see him again. This happened a couple of times - I think it would have been a year otherwise.
He inherited my teeth - overcrowding and overbite, although not as pronounced, as mine have got much worse with age. He now has a near perfect smile.
I decided to do it too and started earlier this year. This was on advice of my dentist, as my overcrowding was starting to cause problems, which I complained about (when I was younger I was told it was purely cosmetic so opted out of train tracks, tooth extractions and other things that sounded highly unappealing to a teenager, for what seemed like not much gain).
I'm now 6 weeks in, and my teeth are already transformed. Less severe overcrowding on top (but it was still bad) is already almost gone, and I can see the progress week on week on the bottom, where it's a lot more severe. And my overbite is already a lot less prominent, and my upper front teeth don't stick out nearly as much. I'm 52, why did I never do this before?
My initial treatment plan is for 15 weeks, so I'm over a third there. It has also involved a number of sessions of filing spaces between my teeth to make space - I believe they call it IPR. It sounds scary but it's minuscule amounts and you don't feel it at all - and it replaces tooth extractions which they used to do in the past.
Depending on where we are at 15 weeks, I'll have the option to continue refining with further treatment at no additional cost. At my age I really don't need it to be perfect, so I'm not expecting to!
My full treatment is over £3000, but as I've so far had over half a dozen long appointments with my orthodontist, including taking moulds, 4 IPR appointments so far and more coming (he does a minuscule amount each time and we're not finished yet, but it takes nearly an hour each time), as well as the actual Invisalign costs - and I'm only a third through the basic treatment, then come follow-ups, retainers etc etc - I don't actually think this is unreasonable. Since starting, I've been seeing my orthodontist every 2 weeks or so. The intervals will get longer once my IPRs are finished, but I have to say, I feel in really good hands.
At the end, I'm also going to opt for teeth whitening as you can use your permanent retainer aligners for this.
I can warmly recommend it if there is any way that you can afford it. And please don't take a chance on something cheap and cheerful for something so important.