Specialist lenders may charge a premium above standard discount interest rates offered by normal lenders. Some lenders will have a set rate for this type of home loan while others assess their risk on a case by case basis for each client and offer interest rates accordingly.
Even though you are not getting the best home loan interest rate on the market, keep in mind that you will only need to stay with the specialist lender until you qualify for a home loan with the normal lenders, at which time you can then refinance to a better home loan.