" Parking in Liverpool costs a fortune "

For how long, where as there are so many options, and what is your budget limit ?

I've often used Mount Pleasant carpark in the city centre. I feel £5 for up to 24 hrs is good value for parking. Scroll down this link, and also bear in mind Liverpool city centre is quite compact and walkable.

https://liverpool.gov.uk/parking-roads-and-travel/find-parking/council-car-parks/

I

We are staying in the city centre for a couple of days. Thought we could park outside the city and travel in. We'll be coming up the M6 etc to get there.

Try Lea Green St Helens just off the M62

Frequent trains into Liverpool

https://www.nationalrail.co.uk/stations/lea-green/

WA9 3BZ

#3 " Thought we could park outside the city and travel in "

You can if you wish, though that creates extra hassle and some costs of train tickets both ways. You would arrive at Lime Street Station.

The cheap Mount Pleasant Carpark is only a short walk from that station, so IMO is a better solution as it's an easy drive from M6/M62 to get to it.

In City Centre Parking terms, £5 per day is an absolute bargain!

There's plenty of free parking at Merseyrail stations but it's for daily commuters. As far as I know none allow overnight parking.

Second thoughts. There's Hooton station, which has a massive underused council car-park that allows overnight parking. Don't know what it costs. Not sure I'd fancy leaving a car overnight there.

As others have said, mount pleasant multi storey car park, £5 for 24 hours, so you can park overnight. There are usually staff knocking about and on the top floor to ask whether you need to return each day to pay or simply once when you leave.

There is a posh and very secure car park at Paddington village, £13 a night.

"Try Lea Green St Helens just off the M62

Frequent trains into Liverpool

https://www.nationalrail.co.uk/stations/lea-green/

WA9 3BZ"

If you click this link it tells you that the car park at Lea Green is closed while they build a new one. It gives St Helens Junction as an alternative (https://www.nationalrail.co.uk/stations/st-helens-junction/) but it doesn't make it clear if the parking is available overnight. I know the Merseyrail ones don't allow you to but this is on the National Rail network so not sure if it's any different.

However, an open return from St Helens Junction to Liverpool Lime Street is £6.20. Not sure how many of are travelling but the "we" suggests OP is not alone so even with two people travelling you'd be saving money by parking at Mount Pleasant. Even if OP was travelling alone I am not sure saving £3.80 would warrant the hassle and extra time involved in getting the train but each to their own.