Even though we all wish to have a perfect websites, sometimes you have to be creative, based on your website you have like 1800 products.

Either you adjust your pricing based on what shipping rates you are using so the second supplier parts are discounted so when your shipping table is used, the customer get charged additional shipping which will allow you to advertise their product cheaper (you sell more of their products, so you will be able to buy cheaper).

OR
Offer Free shipping store wide, add shipping cost to item price if you can't afford to do free shipping.

OR
Use Flat rate shipping, such as Per Category.

There is really no simple answer, you have to get creative and come up with solution.

IMO Free Shipping will be the best solution since you can use that in your marketing campaign.