It all depends on the deals you run across I guess. At the range, you won't notice any difference shooting between a 28 or a 27 of the same barrel length except with the 6" model 27 will probably have a patridge front sight and the 6" 28 will have a Baughman ramp front sight. Both will have the same feel shooting as they are basically the same gun except for finish.

As to finding a nice shooter 28 for under $600; well in today's buying environment you will be lucky in the extreme to run across a deal like that, but I guess it is still possible. For a 27-2 in good shape for a shooter, figure at the minimum $900-1000 minimum. If you open your shopping to later revision, say a -3 to -5 engineering revision, you can probably knock $100-200 off of that number and still get a good quality revolver. I have a 27-5 gun and it's a sweet shooter, with forged internals and decent build quality. I also have several 27-2 guns and I prefer their looks to the -5 gun, but the -5 shoots just as well.