Safest to assume any paint older than 1978 has lead, and paint after 1978 can have lead, it was an additive used to make the paint go on smoother, and was sold in paint stores long after its use was outlawed.
For lead in place you have two options, either get it removed, or seal it in place. Most people go for sealing, which basically means chipping off everything loose and easily scraped away, and painting over it. Wear a mask and vacuum frequently.
One thought, if you get the windows replaced, you also get a lot better climate control, so the cost can be considered in that light as well. Payback time on $3000 would be pretty long, but also helps with resale.