How can I have the default Cost Estimate Type in Items default to Custom? I tried via the UI but that was not an option and suiteanswers gave me the following which I put into a client script on pageinit but that did not work:

function costtypedefaultPageInit(type) {

	nlapiSetFieldValue('costestimatetype', 'CUSTOM'); 

        }

You can only set Cost Estimate type to custom on transaction line items, not on the item itself. It may be hidden on your transaction form as well, so if you don't see it on sales order or something, you'll need to customise the form