VCs don't subsidize the transaction cost (unit economics), they subsidize the (customer) acquisition cost. That is to say, they don't want you losing money on the execution of the transaction, but if the sum total of net revenue from a customer's transactions don't equal the cost to acquire (market, etc.) the customer -- there's the subsidizing.
If you went to a VC with a model for a food service delivery taking less than 30% of the transaction, they'd more than likely pass. 30% is the bar that's been set, and your unit economics have to be as good or better than the existing players. They're not keen on investing in "just a cheaper version of something that already exists." -- If you're marketing yourself as "cheaper," it has to because some innovation has eliminated more cost out of the transaction than you have eliminated in net revenue.
If you went to a VC with a model for a food service delivery taking less than 30% of the transaction, they'd more than likely pass. 30% is the bar that's been set, and your unit economics have to be as good or better than the existing players. They're not keen on investing in "just a cheaper version of something that already exists." -- If you're marketing yourself as "cheaper," it has to because some innovation has eliminated more cost out of the transaction than you have eliminated in net revenue.