Variable Product: if i set variable product and uncheck Manage stock it always shows product is out of stock please check this issue
please edit a product like this below and tell me name of that product
#2. Variable product: With your idea, you need to create unit price, ex: 100$/1kg, then create variation product with options ( ex: 0.5kg, 1kg, 0.25kg). Price on variation will be calculated and auto-update for variation. When update, you only update unit price.