Hi rusty 1,
Have just come across your post and re your question on alternative funding; the rate depends on the type of product you prefer and how your criteria fits. You may want Interest Only, which is available up to 5 years or you may want a higher level of borrowing than the developers mortgage gives you. There are products based on either the monthly, quarterly and annual Euribor and all margins differ.
In comparison you may be aware that there are upfront savings to be had when taking the developer mortgage e.g. there is no stamp duty to pay on the mortgage and no valuation fee to pay, plus notary & registry fees are lower; however if there is a poor rate on offer and compulsory life insurance to take, these savings may not equate to your benefit.
Hope above helps,