Refractor scope minimum specs?

Apologies if this has appeared before - I posted last night, but my
newsreader had a fit, and said it wasnt posted.

I'm after a refractor scope, toward the cheaper end of the market.
What should be the minimum spec I should be looking at?
I'd like to show the kids Saturns rings, and maybe something like the ring
nebula.
What spec. scope do I need to see those?
Thanks
Alan.

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