I've had several pens engraved as gifts for friends and relatives and the engraving has frequently cost more than the pen! So remember that you need to allow a fair bit for the cost of engraving when you decide which pen to purchase. You also need to take care to buy a pen with a surface suitable for engraving.
The cheapest good quality pens are probably those made by
Parker. (Like all of the 'quality' pen manufacturers, they'll repair or replace any faulty pen for the lifetime of the owner). However, because you can buy products from the cheaper end of their range in shops like Woolworths, they don't have the 'cachet' of brands like
Cross or
Waterman (which tend to only be found in quality stationers or in specialist pen shops).
Cross pens are particularly well-suited to engraving. (Companies which supply corporate gifts for executives often choose Cross products precisely because of that reason).
This might help:
http://www.thepenzone.co.uk/
Chris