If you want to keep the cost down, you would have to be prepared to sail at stupid O'Clock.
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Back to 2012 friends had a motorhome and sailed at stupid O'clock.
For me with a clear run the driving time from home to/from Portsmouth docks is around 3hrs but realistically need to allow 4 hours from sailing time, if a time with more traffic 4hr 30min. Hence for say 6am sailing leave at 2am then driving in the dark. To sail late evening then very late checking in at hotel plus gain of cheap ferry offset by an additional night at the hotel. A late sailing to return home again driving all in the dark plus tired.
I've just looked and from Bank of England website the inflation calculator gives 1.19 or 119% 2012 - 2019 yet peak ferry fare increased from ~£120 to ~£220. Your £58 while ~25% of peak fare now is approaching 50% of peak fare in 2012.
Now unlikely I will consider taking the car over until I've retired ( provisionally planned for 3 - 5 years ahead unless pensions & investments still in real terms well below 2019 valuation ) when I won't need to plan so far ahead and can look at mid-week prices.
If I visit before I'll stay in Southsea and hover over to IoW. Other days I can visit the historic dockyard etc.
I note you have given your location as Merseyside so your logical route is M6 - M40 - A34 - M3. Do check in particular the A34 for 8 / 9 / 10 pm to 6am total carriageway closures. In some places the main HGV suitable diversion route can be a long way round and just with a car no straightforward alternatives as when over the years the A34 was upgraded either the old route was used or if cut in half just blocked off.
