The prices have gone nuts. They used to be $3-4 each, which was still pricey, but not worth the trouble of finding an alternative.

Those bolts are M10 x 55mm long. Grade 10.9. I think there is space for a slightly longer bolt - 60mm should be fine.

On McMaster-Carr, a M10 x 60mm flange-head cap screw in grade 10.9, Zinc plated to JIS standards, is $7.58 for 10. (part number 95735A661). This is 1.25 mm thread pitch, so you would have to pick a matching nut with the same thread pitch.

__________________
David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles