I too have been looking into this.
A standard new replacement is quite expensive so I was looking at either a reconditioned unit or get your existing one reconditioned, around £300 I think.
A standard Turbo will cope with the power you want to achieve, with a remap (another £300!).
A hybrid is even more, around the £500 mark but has increased tuning potential, but other parts I'll ideally need adding/ upgrading too.
There a various well known companies who can recondition or hybrid your Turbo, such as cr turbos, turbo technics etc.
Finally you may be able to find a second hand unit for £150 - £200 although you may not be 100% about its condition.
Hope this helps, others may have more detailed info, but its a start.
Jas