Hi Seamus,
I use Antony Lewis' Crossword Compiler and it's (in my personal experience) one of the best on the market.
It's very interactive with more than enough special features with a simple to work way of producing PDFs and exporting your completed work onto the web.
I do know that Don Manley (Quixote, Bradman etc) uses it and also some of the other broadsheet compilers. It also has an update page where you can check out new developments in the programs - some of these updates are free after your initial payment for the package.
Only thing is, you'll pay a bit more than your £100 budget. I paid about £160 4 or 5 years ago and then paid another £50 ish a couple of years ago for a revamped upgrade to the 'Version 9' and I now feel I have enough tackle on it to never have to splash out any more money for the rest of my life.
You can get it by direct download from the internet page or (what I did) get it sent from the USA on a disc so you can put it on all your devices without hooking up to the internet.
It's here and you can trust the site security
http://www.crossword-compiler.com/
Hope that helps you out pal.
Take care, Les40