If you are not going for a forged engine build then engine swap is the way ahead (cost wise) - decent VQ35DE will cost between £750 and £2000 depending on age, condition, mileage and who provides it.
Check with Clarke Motorsport and Zmanalex - both traders on here for a pre-owned engine.
Horsham Developments (Newbury) would be a good choice for an engine swap or any trustworthy local garage - not sure on cost I've seen quotes from £800 - £2000.
to the forum and Good Luck