I also have to '3rd' or '4th' or whatever the count is up to in support of Danner Mag-Drive pumps for return sump duty, or for any duty where the application requires pumping against 6'-8'-10' + of gravity lift plus pipe/hose/filter losses. Every pump in the Danner line-up has a respectable flow rate vs. head pressure curve. But you're correct that these pumps are fairly expensive.
Pentair Aquatics also makes a whole line of Quiet One pumps which are decent, and a bit less expensive than the Mag-Drive pumps. But unlike Danner, only one pump in their lineup ... the 4000HH ... is really designed for serious 'lifting duty' with the rest being primarily circulating pumps.
When you start talking about Rio pumps, these are actually two different product lines i.e. the 'Rio' line of standard circulating pumps and the HF line of pumps. Only the HF line is capable of the head pressures you need for sump pump duty.
The best comparison that I can offer is to guess that you're going to need a pump with a flow capability of around 400gph at 6 ft of head (4 gravity + 2 for pipe/hose friction loss). Have a look at the pump data at
http://www.aquatictech.com/pumps.html and you can quickly see which pumps have a decent chance of meeting your needs, and which ones simply aren't up to the task. Basically all of the pumps which are 'guaranteed' to meet your needs are going to have a 55 watt or larger motor and are going to be rated for 700gph or more of 'free' flow (= 0 to 1' of head).
If you're on a super-tight budget, you might consider a Dolphin (= WP) submersible pond pump. They make a model WP4 with an 85 watt motor which sells for about $30 ! However I can't speak to their quality, but there's usually more than a grain of truth to the old adage that 'you get what you pay for'. The exception to the rule though seems to be imported european equipment, where the quality is usually very good but the price is exorbitant (primarily due to a nasty US$ versus Euro exchange rate right now).
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