Your location would help. Would know something of plant size and your soil composition.
I was born and raised in Seattle where old Rhododendrons are huge and would defeat grapples on all but very heavy tractors.
Where I live in Florida, Rhododendrons are of modest size and most compact tractor grapples could pull them out.
Consider a Bucket Spade if you have a tractor of around 4,000 pounds bare weight. I have used a bucket spade for seven years to remove and transplant 25 - year old Florida Rabbiteye Blueberry bushes as large as Rhododendrons in Seattle, with similar size root balls.
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