Assuming you don't want a pirated copy of Excel, because we all really shouldn't be playing into the arms of the piracy business, short of buying an entire Office suite (cheapest I've seen is Office 2003 Student and Teacher edition for £75-£90, but you may need to prove you
are a student or a teacher), Amazon do a limited availability Excel 2000 package:
http://www.amazon.co.uk/Microsoft-Ex...TF8&s=software
But considering it's nearly £100, you might be able to spend slightly more and get the Office suite.
You might want to consider one of the online versions such as Google's forthcoming online spreadsheet application:
http://www.google.com/googlespreadsheets/tour1.html
As for portable storage, I wouldn't bauly at £75 for a 250Gb external drive, it's a good price. I use a variety of portable drives for backing up and moving my data. I've got a 7Gb laptop drive encased in a portable drive caddy that's been really useful. I've also got a less portable 20Gb 5.25" version that runs off a mains adaptor. But for really small and quick transfers, I use a 256Mb USB memory stick.