Effects of rust on steel frame strength

The rust seems to have a relatively smooth surface, no pitting, no flaking. It looks like surface-only rust. Personally, I would clean and repaint, taking the risk.

Depending on your tour (close to civilization or not) or if you want to be careful, check out your local bike shop -- they might have an old fork somewhere that will fit your bike and cost less than 20$.

Consider using rust converter before repainting the said area. From the picture, the rust doesn't look to be that bad since pinholes haven't formed and the surface is smooth.

Sand the rusted area down and apply a bit of rust converter. For primer, you could use epoxy which works better and is a lot better for wet conditions. Polyurethane paint also works well for steel bikes exposed to harsh elements.