Genuinely, it all depends.
Every business is different and every SEO situation is different, so I quote for every job.
I don't wish to be controversial on this point, but in the professional SEO places I hang out in, package prices are "where bad SEO hides".
Anyway, it's really not for you to have to choose between packages. Do you really understand SEO? I work hard to, it's my full time profession. It's for the SEO expert to assess your situation and put forward a credible plan to bring you profitable business through search.
For example, I'm presently working on a client whose main search phrase gets 13,600 searches per month in the UK, for which people are paying £4.10 per click when they advertise. Someone's making money.
Maybe it's the company that's taking 38% of that traffic. They have 520 relevant pages. The next biggest competitor takes 18% and they only have 61 content pages.
So perhaps we can fairly quickly take second place by writing .. it may as well be 100 .. quality content pages. How does two per week sound? So long as that second place company is slower than our new SEO plan and doesn't see us coming, we should catch up.
That comes from search analysis, looking at the sort of questions people ask, acknowledging your assets (especially your people, their knowledge and experience) and knowing your competitive position (for instance if you're a high end art gallery we're not going to write SEO articles about where to get art on the cheap, we'll talk about investment and quality and backstory).
Another thing to consider is your clients' value journey, or your sales funnel. There's content to draw people in. Content to help people make a decision. Content to improve their satisfaction after they've bought so they recommend you and write testimonials.
So, we can make a plan. You could farm out your writing to some factory in Indonesia and get it all written in five minutes for 50p but guess what? It will be garbage. I know one place that outsources content to India, to a presumably quality place they have a relationship with, and the UK team spends all day with the content they've been sent, editing it to make sense.
I've a better idea. Get a really good writer (me, I mean .. just as a crazy example) to write something characterful and engaging that your people will enjoy reading. If they find your material informative, if you use their language, if they feel like you care and your business stands for their values, they'll bloody love you, because .. just look around .. God knows we all need something good to happen. "Someone on my side? OMG, let's go!"
What happens then? Your People share your content to Other People Who Are Like Your People. Google sees those shares. They think "hmm" (AI bots are always doing that) "hmm, if people are sharing this article, maybe these meatheads actually like it, I'll raise it higher in search and see what happens".
So, two takeaways*. The first is, everyone is different, so to quote for your SEO I need to pop in to your world, run the numbers and make a custom plan. Don't be a sausage in an SEO sausage machine. ("Don't be a sausage" works more widely if you're ever looking for a new year's resolution or t-shirt slogan.)
The second thing is .. SEO is competitive. There are only ten slots on page one, and seven of those don't really represent success, ideally you need to be in the top three. So, you need to hire an SEO gladiator. Buying cheap is a really bad idea.
SEO is an online battle with real cash winnings. You need someone good on your side.
So now I've made myself look conceited and cocky. I'm a thousand percent not like that. But I have worked on cheap contracts before and it's not good. You live and learn.
I'll mitigate the whole gladiator thing with this. The SEO cost is as flexible as your goal. Let's talk, and we'll cut our cloth. If you want to get into a competitive search phrase for £100 per month, the answer is no .. but .. maybe we can start by using SEO to turn a profit in a sub-niche in that market. Then re-invest and take another niche. Collect niches until we have a .. actually I don't know what a collection of niches is. Maybe we get the whole market.
Anyway, the answer to How Much does SEO cost? is .. give me your details and I'll lay it out for you.
(You could check out my page on SEO companies and you'll see, actually, SEO can actually be fairly quick, easy and low-cost if you know what you're doing.)
* I think I must have been starting to get hungry at this point