Holyhead to Aberystwyth

To do the whole journey by train, you will need to travel into England & then back out west from Shrewsbury. Fares and schedules for your date have not yet appeared on the system and engineering work may be taking place on a Bank Holiday. So, try this site in about 2 weeks to see what the situation is regarding your date.http://www.nationalrail.co.uk (Pre-booking is usually cheaper as prices are likely to rise as date approaches - so check for dates like tomorrow to see the difference - if any). Where engineering work does close lines, the train company will provide a bus alternative.

This site may be able to provide you with a cheaper foot passenger (on the ship) & rail fare combined.
http://www.arrivatrainswales.co.uk/SailRail/

A shorter bus route does exist but it probably does not run on a Bank Holiday. www.traveline.info

You may also wish to do a search on this site to try and find a car hire company that can deal with you on the Bank Holiday Monday at Holyhead.http://www.travelsupermarket.com/c/cheap-car-hire/uk/

Thank you James for your quick response. We had no luck getting a car rental on the Monday which is why we are heading to Aberystwyth. We want to bus through Snowdonia so hopefully that will work out. Thanks again!!

I take it that you wish to see Snowdonia en-route? The buses (I think) tend to take a less scenic route between Caernarvon & Porthmadog. If you can get from Holyhead to Caernarvon - which has a fine Castle; consider taking the Welsh Highland Railway through the Snowdonia National Park to Porthmadog. http://www.festrail.co.uk/timetable-whr.htm

If you could stay 1 night in Porthmadog, you could visit nearby Portmeirion. Anyway, from Porthmadog to Aberystwyth, you can continue by bus or train. (Minffordd is the station just over a 1 mile walk from Porthmadog - it has 2 stations - narrow gauge steam train and normal gauge for the line going south). The line south hugs the Cambrian Coast and is very scenic. You would need to change trains (for Aberystwyth) at either Dovey Junction (in the middle of a vast marsh) or Machynlleth. www.nationalrail.co.uk for schedules.
http://www.portmeirion-village.com
http://cadw.wales.gov.uk/daysout/caernarfon-castle/?skip=1&lang=en
http://www.eryri-npa.gov.uk/home

From Aberystwyth, consider a trip on >http://www.rheidolrailway.co.uk

Thanks again James. Unfortunately we have just the one day, May 25th to travel from Holyhead as we are booked into a B and B in Aberystwyth that night. Looks like we will be bus/train hopping that day!!