Is there any benefits of going for plant hire company than buying new machine?

Please clarify your situation. I think I can guess, but without a detailed analysis of your company, the product, and the cost of the machine, we can't possibly answer this.
If this is a homework question, you need to work on it yourself first.

Do you mean outsourcing to cut costs as opposed to high initial investment in upgrading equipment? What did your cost benefit analysis reveal to be your timeline to recoup from that investment?

As noted, any purchase of equipment needs to be justified with a ROI statement and long term projections

NOTE-ROI, is the return on investment.