Firstly Hello & Welcome to STB Carl.
Yes you can go & buy the S400 (my lad has one) as it's a very capable rifle, light & easy to maintain.
I always try & buy the best I can afford at the time or save up for longer, don't forget about the other things as well like scope, bag or case, mat or bean bag, filling bottle, clothing etc as it does soon mount up.
I knew when I started shooting again I would enjoy it so I opted to buy the kit I have as I didn't want to 'sell & upgrade' later on, in a way it saved me £'s.
With the S400 I would look for it in a better stock than the beech one as it's very basic & not good for FT if your serious.
An MPR may be a better choice but doing some homework first always helps you make a good choice in the long run.