I was in a similar position (i.e. wanting my first road bike but not having a huge budget) back at the end of May. I opted for the
Triban 500SE in the end, which cost me £330 but the price has now gone down to £299.
It might not be the greatest bike in the world, but at that price it feels like a steal. Well reviewed by sites like road.cc and cycling weekly it has perfectly suited my purposes - e.g. commuting to and from work every day and a few times a week going on longer cycles between 20 and 60 miles. Not had any real problems with it, in fact the only one I had was very quickly and painlessly fixed by taking the bike to my local
Decathlon (the gears need a slight adjustment, but apparently you should do that shortly after buying any new bike as they 'settle' in and shift slightly).
A word of warning though: buying the bike is only the first step in a new journey of ridiculous expenditure, consumption and, for me at least, addiction. I've probably spent at least one hundred, if not more, pounds on accessories, tools, and other bits and bobs. Totally worth it though, any day now that I don't manage to get out on my bike I'm left feeling restless and desperate to go have a spin around.
When I eventually come to replace it (not any time soon) I'd probably try and go for a second-hand slightly better model, but as a novice bike user/owner having the ability to go to Decathlon and get it fixed for free for the first 3 months at the very least is also a useful safety net.
Also, they don't give me a commission on saying how great their bike is but they bloody well should as I've convinced at least 3 separate people to go out and buy one...