How to get from Canbridge to Dublin?

Caveats:
1. Rental car to return in the UK
2. Have to be at Dublin airport by 6 a.m. on Monday
3. Low cost is a good option
4. We'll each have luggage, at least one bag or backpack each 40 - 50 lbs. + something smaller.

Option 1
Searching the Internet I read about a Rail Sail ticket from select stations to Holyhead and a ferry crossing to Dublin, priced @ 35.
But when I searched 3 different train ticket sites, the best fare was 80 at 8 a.m. and  up to 100 for later trains. The closest station to Cambridge was London Euston.
The rental car could only go back to one of the airports.
Stansted is 34 minutes from Cambridge. There is a train, the Stansted Express for 20 that connects to London Liverpool.
London Liverpool is 20 minutes to Euston (I suppose if one know what one is doing and has tickets in hand). One exchange.

So that would be a Sunday morning drive, drop off a rental car, navigate the airport to the train, change lines in London, change again, navigate Euston to Virgin Rail, transfer at Holyhead. I didn't work out exact times but it would be after 5 p.m. at the earliest to Holyhead. Cost roughly 240 for 2, not including London subway. All of this done hauling luggage.

Option 2
What about driving to Holyhead? 4 hours roughly. The rental car needs to be turned in before noon on Saturday (although I wonder if possible to drop off after hours - need to check just in case we are late). No extra costs for the rental car other than fuel.
We'd need a place to stay in Dublin one extra night.
It would probably be a good idea to leave Saturday and have all day to drive to Holyhead,  which would mean finding somewhere to stay Saturday night in Wakes. I think we could manage that for less than 240.

Which will it be? An Amazing Race dash across England? Or a relatively calm drive exploring where our hearts tell us to go with two possible crises (finding the car drop off and before it is late)?