Roughly how much should I expect to have to spend for custom cooling loop?

Im looking to run 2x 420mm radiators for the cpu and gpu. Im wanting to go with hard line tubing in an O11D XL case. Im aiming to spend about 3-4k (NZD) on the actual components and im not quite sure how much doing a custom loop would add to that. For context im planning on going with a 9070xt + 9800x3d (potentially a 9900x3d depending on the cost of the loop).

Also any recs, tips and things to avoid would be very appreciated.