Hi seagull .. I'm not sure how the ticketing or pricing would work, but the destinations which you have given just as an example are not on the same route or service. Altea for example is on the Alicante > Benidorm > Denia line.

For route maps and timetables, you may like to take a look at these individual wesbites:

TRAINS / TRAMS (LOCAL)
Ferrocarrils De La Generalitat Valenciana (FGV)
Services from Alicante to Denia via Benidorm
http://www.fgvalicante.com/page.php?idioma=_en
Tel: 0034 96 526 27 31

TRAINS (NATIONAL)
Renfe (National Railways) Alicante
http://www.renfe.es
Tel: 0034 902 240 202

David

When are you visiting Spain, if its in the winter you could buy a weekend tourist rail ticket which gives you unlimited rail travel between Alicante and Denia.Not sure about onwards to Valencia though.