I would consider Sarah's show to be on par with the "Real Housewives" series(es) in the US. The Real Housewives of NY get paid $10,000 per episode, a payraise from their first season of $3,333 per episode. The real payoff for anyone on one of these "reality" series is exposure, to introduce them or expand their visibility. In other words, it's to market oneself to a wider audience and hopefully parlay that exposure into bigger and better things.
Sarah's a bit of an anomaly in that regard: she's been well known for a long period of time but that has been fading. (By way of reference, I work in an international finance firm, and my team consists of twenty-somethings who report up through several levels to me. We talked about the Royal wedding because at our Friday meeting on that day, I asked that scones be substituted for bagels to "celebrate." I had to actually sit down and explain to the under-30 set exactly who Sarah was; most had her confused with Camilla or, honestly, thought she was dead. Mind you, we hire the absolute cream of the crop each year from top schools, so these are not under-the-rock specimens.) So - Sarah might have been able to command the top end of the reality show pay scale per episode - let's say $10K per - rather than the low end of the scale.
The core cast of the Jersey Shore got popped up from $30K to $100K for the new season, but the ratings on that show are many multiples of Oprah's show. Any of Oprah's shows.
So if I were to guess, I'd say $10K per show for Sarah Ferguson, with the upside for her being the exposure and hopefully the impression to potential investors in Brand Sarah that she's turned herself around in a meaningful way.