Since you're planning on re-siding, this would be a GOOD time to have insulation blown in. 1) It should be less expensive since there's no 'finish work' other than covering up the 'blow holes' with your insulation board. 2) It will be quick since the work is being done from the OUTSIDE instead of the INSIDE of the house.
If you don't have the $$$, try to borrow it from family or get a loan. You'll be surprised at how much $$$ you'll save with having the insulation. You'll actually be able to take the $$$ you've been spending on heat and make payments! Yes, until you pay off the 'loan', you'll pay good money for a while. BUT, the great news is you'll be done w/it in a few years, and then you can take those 'payments' and start a Retirement Account.
As 'bc' says, believe me too, it's the ONLY way to go. My best to ya and hope this helps.