Forged motors if built properly and mapped properly and well maintained and driven properly should be extremely reliable and provide loads of fun and longevity.
However, the cost of maintenance will vary greatly depending on whether you are planning to be a regular track day warrior or just fast road use.
Depending on what power and to what extent you track the car then you will have regular financial outlays.
Remember that every time that you "tinker" with the motor then you will probably require a tune.
It is very important that your tuner/mapper can provide fast, professional, remote mapping if you are not close to a suitable mapper.
Your choice of mapper will depend on your location and what ECU you run with.
My 720 bhp/710 lbs/ft track 350Z is running Syvecs S6+ remotely tuned/mapped by Abbey.
My 840 bhp/700lbs/ft track R35 GT-R is running Ecutek remotely tuned/mapped by Litchfields.