Getting a 5 year rental agreement in Spain and especially Benidorm can be a problem but not difficult. The main problem with a 5 year lease is that Spanish law is on the side of the tenant and with 5 years it can be difficult to get tenants out of properties. You will find most landlords will only offer an 11 month contract at first until they get to know you. Many landlords in Benidorm are not over trusting to British tenants. The town tends to have a very high turnover of young and unfortunatley irresponsible tenants who fail to pay rent on time and leave properties in disrepair - they have made it a little difficult to secure long term rental agreements.
You should also consider with care where you are to live Benidorm. It is very crowded during Summer months and noise is a problem in the center of the city. You may like to take a look at La Cala which is quieter and cheaper than Benidorm but only ten minutes drive to town with a good bus service until late and all night in Summer. There are some good Spanish agents in the bay who look after rental properties.
If you do secure and enter into a long term rental agreement using a lawyer to check the contract details, debts such as electric and water bills are up to date is essential and don?t part with any monies until your lawer says everthing is OK. Be aware some agents will ask for up to 2,000+ euro commision for finding somewhere to rent - it is not necessary to do this so avoid these people. A commision of one months rent is more usual with repuatable agents. You should also ensure your agreement has a termination notice of at least 3 months should the owner decide to sell the property. Although with a five year contract you would have first refusal to buy the property - the landlord would have to give you 30 days notice to offer you the property before offering to another party or begining the termination notice.
Long term rental in Spain is much lower than other EU countries and to combat this the goverment has set up the Sate Property Rental Agency which has been open for a year they have a website in Spanish at http://www.spaviv.com/ If you do not read Spanish you will need a translater. The owners of properties on this register are commited to fair contracts and fair rents.
For a list of English speaking lawyers in Benidorm see this PDF file online http://www.britishembassy.gov.uk/Files/KFile/lawyers_spain05.pdf
