Joomla 4 is approaching its official release, and can be expected before the end of the year. I won't be updating any sites initially, as I like to let it settle in as there are often a few releases in quick succession as things get ironed out. It's a major release, and the last major release (Joomla 3) was September 2012 - so it's been a while! Joomla 4 is not compatible with your existing site, so it's not the usual quick update between versions.
Firstly, the template that your site uses has to be upgraded by the developers, and released as Joomla 4 version. Parts of the functionality will be rewritten, for example, RokSprocket will no longer be available and will be replaced by something else. So, when I upgrade the site I may also have to rebuild parts of it, replacing the old functionality (slideshows, lists, service blocks etc) with new equivalents.
Most of the templates that I've used for sites will be available as Joomla 4 versions, but there are a few of the older ones which are not going to be available. In this case we'll have to choose a new template for you site, but chances are that if it is that old, it's time for a bit of a refresh anyway. Likewise, even if your current template is going to be available for Joomla 4, you might like to take the opportunity to incorporate a fresh new look.
Secondly, the components that the website uses must be compatible with Joomla 4. That's the backup utility, the security utility, the editor, the optimisation (page speed) utility, blogging utilities, slideshows etc etc. If any single software component isn't compatible we'll have to wait to upgrade later, or find an alternative component to use.
Thirdly, the actual update. What I will be doing is making a copy of your website, and doing the upgrade on one of my development servers. As I have about 60 sites to do, it will be a straight 'same for same' type of upgrade, and then I will overwrite your existing website with the new Joomla 4 version. I won't be able to wait around for weeks while you get those photos that you want to add.... but I will be able to do it later, once the new site is live.
What will the cost to you be? As each site has different requirements due to the template it uses, the extra software components it has installed etc etc, the price will be different for everyone. As Joomla 4 hasn't been released yet, I don't even know how long it will take me to upgrade a site because I can't do one yet.
When will it happen? Well, the good news is that Joomla 3.x will continue to be supported for two years. Of course, I can't wait two years and then try and do 60 updates in the last month, so I'm going to have to stagger them. My plan is to start with the oldest ones first, and make my way through the list, tackling the newer ones last. When your opportunity comes up, if you are too busy and decide not to proceed, then it may be a while before I get back to you on the second pass through - like, we may have entered into the 'not supported any more' phase of Joomla 3 where it will still work but there are no more security patches released and eventually it starts breaking.
Moving to a different platform. If you'd like to move to a different platform (maybe you've heard your friends or associates talking about Wordpress) then I can do that instead of Joomla 4. Although, this time around for any change of templates in Jooma, I'll be using a page builder, which puts all content in the article, and eliminates the need for diving around in the backend of Joomla trying to find modules etc. It's pretty cool and I think you'd be happy with it, but it's up to you.