Yes.. there is a difference. You can pay in the 1000$ range and up for a 5' rotary mower from a good brand.. like NH, JD, Bush Hog, schulte, .. etc. And they are like tanks.. and heavy.
They perform and last a long time if use correctly and cared for.
That said.. you can get a light to medium duty 5' roatry mower in the 500$ range. Not as heavy duty, and not as heavy. Usually the sheet metal is thinner, as well as the braces.
Sometimes weight works to your advantage. i do alot of mowing with the antique tractors I collect. While they have the pto hp for a 5' mower.. some of them have hyd capacities limited to 800# on the 3pt. I've seen 5' rotary mowers they simply couldn't lift.. or if they did lift it.. the hydro pump was drawing way too much hp away fromthe engine...
For occasional cutting.. I'd go light duty. If you plan to buy then sell.. you'll take more of a money loss on the high priced unit.
I've cut for 4 seaons with my 5' KK mower.. 13 ac at a time... -0- problems so far. I also have a 10' howse.. which addmitedly is part of their heavy duty line ( heavy duty line at from an economy brand.. almost sounds funny.. ) It mechanically works great.. though i need to get used to mowing with a 10' multi bladed mower rather than a 5' single bladed mower.
Also.. if you sharpen your blades a tad.. and cut often.. a rotary cutter will make a decent cut, and almost make a lawn apperaance.. more like a shaggy lawn.. etc.
Soundguy