I don't know how much lessons would cost near you, but around me a group lesson is about £25-30 an hour. If you can't afford that, then being blunt, you can't afford the cost of a horse, even split 5 ways, especially on full livery.
The initial outlay for the horse is also more than just the purchase price. You need to budget for a vetting (£300+) and probably at least one failed vetting too! Some horse are sold with tack and rugs, but a lot aren't- tack will probably set you back £1000 at least, and rugs + basic care equipment could easily be another £500 (if not more). So if you assume a purchase price in the mid 4 figures bracket, plus buying all the other things you will need, that will easily cover a year of lessons, and that will put you in a much better position to be able to buy.
My pony (who is pretty cheap to keep) probably costs about £500 on DIY livery. I'm happy to give you a breakdown of costs for this if you're interested!
As a complete beginner, riding unsupervised would really be quite dangerous, so once you have the horse, you would need lessons anyway- so why not get the lessons now (once every two weeks, or once a month if that is what you can afford) and then save up for the horse in the future. Also, depending on the full livery, they may not be willing/able to teach you everything from scratch, so you may not learn to care for it as quickly as you think.
Do any of the five of you have experience with horses? Realistically, size and ability wise, would the same horse actually suit all of you?
Buying a horse is a nightmare at the best of times, let alone when you are really inexperienced- people really do lie, and one person's idea of a "novice ride" is very different to another's.
I fully understand the desire to have a relationship with a horse, but I would honestly get some riding and stable management lessons at a riding school first!
I also think sharing one horse five ways would be a potential for real major fall outs:
-What if the horse got injured whilst in the care of one person?
-What if you disagree about a medical decision like colic surgery or box rest?
-What if (worst case scenario) there was a catastrophic accident and one of you had to authorise PTS without the others present?
-What if the horse proves unsuitable for one or more of you?
-What if one or more people lost interest and pulled out? Or had to pull out for financial reasons?
-What if you disagreed strongly about how the horse was kept (e.g. barefoot vs shod, individual vs group turnout, in at night vs out 24/7)?
Even small things could cause major fallouts- like breaking equipment, or someone not doing the care exactly how you would like it, or someone wanting to use an instructor you didn't like, or disagreement about different riding styles etc?
If you hit any sort of problem with the horse when ridden (or stabled) e.g. napping, bucking etc, then there could be a lot of disagreement about how to sort this out?
And buying a horse to suit 5 people is bound to cause disagreement!
I'm sorry to put a dampener on all of this- but honestly, find a way to invest in some lessons first, before you think about buying!