Replace old windows in cinderblock house
It sounds like your situation could get quite involved. I would get some quotes from window companies that do the whole job. Get more then one quote and don't just pick the cheapest. Make sure the they are including finish work inside and out. Ask about how much they may expect a quote to vary. And if there are any similar completed jobs that you might be able to see.
A Cinderblock construction will most likely require many custom sizes and you want them to be responsible for measuring and stuff. So when they install they can't blame your measurements! Other wise you may be buying window that won't fit.