If you're going to be doing a bit of decking then you'll want a say that can cut 90-95mm thick, won't you? That would mean purchasing a saw with a 12in/300mm blade. Some of the 10in models will just about cut 90mm. There are also plenty of non-sliding saws available that will do this - though, you'll want to check the maximum cross-cutting capacities with the blade at 45°.
The better the saw, the better the laser, is generally the way it works. They're not 'essential' by any means, if the pre-set stops on the saw are good. But, if you're looking to make compound cuts, aligning the blade to a pencil line then, they can prove invaluable for this (much easier than trying to 'roll' the blade along the line...).
I'm a big fan of the Makita saws. I've owned the 10in LS1013 model for a while now and, even though it was second-hand and had plenty of use on site previously, it cuts very accurately and the results are repeatable. Unfortunately, their saws would be way over your budget - unless you could get something second hand on eBay? Newer models now come with a laser, meaning the older ones can be found a bit cheaper.
If you are looking for a new saw though, Axminster have
this one on special offer (it's bang on your budget). It slides, has a laser and everything else... Would the 90mm depth of cut be sufficient?
Axminster don't seem to have any 12in sliders in their own brand but, the SIP range looks quite similar and they do have their own 12in model,
here (it is above your budget).
I've not used saws from either brand but, if did a search of the forums, you'd find that people have had good experiences with the SIP saws in the past and Axminster's own brand usually isn't too bad. It is generally a case of 'you get what you pay for' with these things but, if it's only for occasional/DIY use...