I have an old pair of Rossi road touring boots which I find are ideal for my dirt track efforts.They are light 3/4 length quite flexible padded fairly well and I haven't worn the soles very much, the tread has worn off the left boot and the sole is very smooth now and slides easily. ( I don't put much weight down)
With a pair of shin/knee protectors slipped down the front (skinny legs) I feel wellprotected there.
AND I got 'em 2nd hand for $50 I have a pair of full length motorcross boots but only wore them once, too hard to change gears.
cheers pancho.