The Premise

Setting a near-ish future world, where people live a full life and then upload their minds into different hardware and continue on.

Setting a timeline for this, when (what year) are we looking at? Note that the development is an ongoing process so initially it becomes technically possible^"», then the rich can do it, and eventually white-collar workers or retiree's can do it.

Hardware

There are several issues. First is the hardware. The needed hardware is discussed in this (sadly under-rated) answer. Taking as a baseline the spiking network implementation of a neocortex, add some overhead to handle porting an existing mind. That is, it will need flexibility to adjust the cortical columns to match what had grown in the brain, and there may be additional ad-hoc mechanisms needed to make the feedback and control work exactly like the brain rather than a clean designed implementation. But it would still be more efficient than simulating individual brain cells, or at least require much less memory.

So figure 10¹⁹ flops, but only 4 to 40 Tbytes of RAM to hold the state of all the pattern matcher complexes (the figure is sensitive to the degree of fan-out among the pattern matcher units) and double that for the loose individual nurons and ad-hoc stuff that doesn't fit the model.

The Costs

The new post human will need to have this measure of compute resources dedicated to him, whether owned, leased, or rented; so the cost of that comes down to him. Certainly it's worth taking out a mortgage for, or saving up for. But consider the equipment lifetime and the earning potential of the post human using it. Although the price of an upgrade will drop years later, he needs to sustainably afford to keep hardware.

Next, something that I don't see considered in this kind of fiction! The cost of energy to run the brain! The first usable exobrains will use much more power than the old brain, so grocery money isn't enough to keep it going.

The growing population of post humans may have a larger energy demand than they did in their biological life, and this is an interesting societal aspect to explore. But in this question in particular, the post human needs to afford to "eat". This is an ongoing expense that goes with his uptime.

People in this state might be earning based on saved capital, but as it works down to more ordinary people, we need his earnings as a post-human to sustain his expenses.

misc

Meanwhile"¦ fiction often portrays AI and uploaded minds as being enormously faster than life. But I think they will initially be slower! If the upload runs at a fraction of the speed of his biological counterparts, it will affect his ability to work job and amplify the electricity cost per consciousness-hour.

I suppose that virtualization of environments and connectivity will be cheap enough locally (within the post-human living center) that it's included in the power cost. Connectivity beyond his home center would be the same as any network access costs.

Finally, there is the one-time expense of getting scanned and uploaded. That is something that can be dragged out as long as needed since it is a one-time and not reocurring expense. As long as the post-human can earn money (whether by working or ownership) this won't be a limiting factor.

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The Question

So, what future timeline are we looking at for the phasing in of post-humanism? When will it be possible for the rich-enough, and when for middle class first-world citizens?

Consider cost of the exobrain and ongoing running costs, compared with people's ability to afford that before and after porting themselves.

If the idea of mind uploading is so distracting that you can't help but to react to that instead, try to forget that and consider the question to be "When will people (of various economic) classes be able to afford to finance and run a computer of the stated power (when they won't have normal expenses of housing and food, either)?"

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Footnote

"» The existence of destructive scanning technology can be assumed as part of the story. It will simply be there once there are computers capable of handling the data.

Likewise, getting potential customers to accept uploading is a different topic from this question.

Clarification

Please note what the question asks. (why do I need to say this?!)

It is not: propose a different story, repudiate the premise, riff on what posthumanism is like, repeat the linked hardware discussion, "¦,

Read what's already been discussed if you have a comment.