Nel or net fella? I only ask because nel is 120 bhp isn’t it and net is 140bhp?? EBay should get you either reasonable price and if it’s service exchange even better, failing that try your local motor factors.
There’s a net on eBay @ £250 from astra 1.4 turbo, possible head gasket fail and another with noisy chain from a gtc £700. Given I’d be thinking of doing gaskets, chain and water pump before putting any new engine in, the astra one @ £250 might be the best option.