AncestryDNA has a special offer running for Mother's Day, which is next Sunday (26 March) in the UK and Ireland.The offer is already live, and will continue until the day itself.
The discount brings the price down from €95 to €80 or £79 to £69, and shipping is payable on top. Shipping costs €20/£20.
Ancestry's landing page has a good FAQ and general introduction to DNA, and the real-life examples should help you ascertain where a test may prove useful to your own genealogical research; it's worth reading if you're hesitating to take the plunge.