I picked up a More Miles Tri Suit on
eBay for about £30 (like this one
http://www.ebay.co.uk/itm/290716981756?hlp=false#ht_1984wt_1253)... which is super cheap for a tri-suit. This one got Top Value Award from this
http://www.triradar.com/gear/tri-suit-reviews-under-80/
Father Christmas brought me exactly the same trisuit. Having used it for my first tri last weekend, I can vouch for it being an excellent bit of kit.
When I arrived at the start, the car temperature gauge was reading 2C. I was somewhat concerned about exiting the nice warm pool into such chilly conditions at 7.30am, and accordingly left several extra layers in my kit box in transition - a cycling top, a windproof gilet, knee warmers, arm warmers, gloves, skullcap, socks...
In the event, I didn't need them - I was more concerned with just getting out of transition and on with the bike leg. Well, I put the windproof gilet on, mainly because there's a long fast descent shortly after the start of the bike leg, but I had to unzip it fairly soon because I was getting too warm. I think the adrenalin helps keep the cold off, not to mention the fact that the level of effort you're putting in (or should be putting in) also raises your body temperature pretty quickly.
Despite the cold, the trisuit dried off pretty quickly. I can also vouch for it being equally comfortable for swimming, cycling and running in. The only caveat is that it has very light padding (I believe this is standard for trisuits generally), which is fine by me but might cause problems if you like a lot of padding in your cycling shorts.