Thanks for that.
I was able to book ok yesterday, for info if you go on the renfe site and hit the 'return' button then on the drop-down put alhama de murcia first then Valencia and the dates, it will then give you detail of a direct service.
You will be offered 4 different types of ticket, the cheapest was a promo& but for that one you can't reserve seats etc. For an extra few euros you can reserve seats.
The rest is simply payment details etc, then you can print your tickets directly.
Our trip cost 92e return for 2 people which I think is pretty good, the times are also excellent leaving alhama de murcia at around 8.55 and the return from Valencia 2 days later around 15.30.
Both journeys just under 4 hours.
A lot of the hotels are close to the train station so the whole thing easily planned.
If anyone needs anymore info they can message me. John