just come accross the Eyewitness Arabic Phrase Book:

http://www.dorlingkindersley-uk.co.uk/nf/Book/BookDisplay/0,,9780751321586,00.html

Seems to be a pretty reasonable price too?

try whsmiths website, they are selling the berlitz arabic phrase book for £2.99, with free delivery to local store.
Although tunisians speak arabic, its a mixture of french & arabic words, rather than classic arabic.
hope this helps

I've had the Dorling Kindersley book for ages and it is very useful, as not only is it cheap but a good size to slip into your pocket or handbag. Incidentally, Linguaphone are doing a PDQ (Pretty darned quick) Arabic course on 4 CDs, with an illustrated book for £19.95 + £2.99 postage until 30th October - phone 0800 177 199.

http://www.greatwaytoarabic.com/

Im using "Arabic for dummies" at the moment.Its quite a straight forward book, and relatively easy to follow.

However, I can highly reccomend the 'before you know it' course which is a free 'lite' version available for download here -

http://www.transparent.com/

Ive found it a very good way to learn the basics of Arabic