Non road biker needs bike
From what you say, I assume you are just going to use the bike for training - including winter training.
Clearly there is masses of choice for road bikes. I have bought couple of great bikes on ebay - one from someone who spent £3500, then added £1200 for some lovely wheels, rode it for 50 miles, then left it in his front room for 18 months before selling for around 25% of what he paid.... these are mid life crisis bikes and can be a bargain. My second bike was a TT bike from a lady who got sponsored after the first 2 events of the season - fantastic bike at 30% of new price.
The most important consideration is fit - make sure that the bike fits well. As a general rule, a good Alu frame is better than a cheap carbon frame, do not rule out an Alu bike.
However, for you, I am going to make a slightly odd suggestion - how about a CX bike. I have just bought a CX bike with a 1x11 setup 44 front and 11-36 rear and disc brakes. Yes I know that it is not as fast as a road bike... but not by as much as you would expect, especially with a set of 28mm tyres. It is awesomely comfortable, and great for riding in the winter with wider grippy tyres and disc brakes. And you can take it off road as well, and do some CX competitions to get fit. Next year, you can get a TT bike for your IM, and with a TT bike, CX bike and Mountain bike, you have all bases covered
In addition to Matthew's comments, I would say that it will depend basically if you are planning to make this IM race as only one time adventure, if so, you should think in a second hand TT bike (low cost) as Matthew's recommendation. But if you are going serious on long distances triathlons, then, you better think in a bike fitting session (very important, in order to get your stack and reach measures), after this, you can choose a good carbon frame, good groupset and wheels, but all this will depend of how much are you willing to spend, you can have a new TT bike from 4,000 usd up to 15,000 usd (or even more). There are several nice brands with amazing bikes like Cervelo P5X, Dimond, Canyon, Pinarello Bolide, etc. If you are going to a top range bike, I highly recommend to buy all parts separately so you choose the parts you like and save some money. Good luck !!!
If you only been riding MTB then I think a road bike would be better for you than a TT bike. Then after you get use to riding road, a set of clip on aero bars and you good to go for IM. You should be able to stay within your budget for a road bike but the most important thing is that the bike is the correct fit for you so worth checking out bike shops for their advice on sizing. I'm an Xterra competitor and riding road definitely helps my off road speed.
Good luck in your bike search and hope you enjoy your Ironman journey.
Going to piggyback on this thread as I'm having a similar(ish) dilemma...
I'm looking at buying a bike for my first IM (Bolton 2018) and am torn between an aero road bike or an endurance road bike.
My thinking is an aero road bike is going to be a halfway house between a TT's efficiency & relative comfort of an endurance bike. (I'd go for a TT but want something I can use outside of Tri's).
My problem is I've not really ridden much before so is jumping straight on an aero road bike a mistake vs an endurance bike? Would an aero bike be unforgiving for a noob over 112 miles vs an endurance bike?
Essentially I want the best option to get me to the finish (efficiency of an aero for the legs vs the comfort of an endurance to help me survive intact!).
For the record the aero bike I'm looking at is the Giant Propel Advanced 0/Pro. Good choice for a rookie?..
Thanks in advance, all advice gladly accepted.
Grant King, that's great, thanks!
I was worried it would be too stiff and unride-able for me so this makes me feel MUCH better.
I'm pretty keen on the Propel and there seem to be quite a few price/equipment levels so looks like there's a lot of scope for future upgrades etc.
Thanks again for your advice.
Im also a complete newbie to Triathlon and also fancy an Ironman next year in Lanzarotte, I came from a modest mountainbike background and after a few test rides and speaking to various dealers opted for the Giant Advance Propel 0. I love it and on the few sportives ive done so far its a popular choice, I was worried about comfort, but besides neck ache (lesser as the miles build) its great. I bought it late July and have covered over 500 miles so far with a 62 and a100 mile sportive and the Lanzarotte Iron man route, its a very popular bike, many happy owners and very glad I plumped for it, my local Giant shop is great with advice and set up, I cant recomend them enough, only problem is I dont think they do them in a ladies, they have an equivilant I believe in the LIV range and there a bit over your budget, but I felt buy once and buy a bike that can do everything I need . Good Luck with your first Ironman Emma