I know the Zeiss Softar filters are highly regarded as tops for portrait photos, unfortunately they are priced to match, and currently out of my photography budget.

I'm looking for a lower cost alternative. I found the Tiffen Softnet series of filters. Does anyone have any experience with these?

Any other suggestions?

I would stay away from the Softnet filters. I you shoot with them at small apertures you'll get the pattern of the net in your photos. I've always just used acetate between a cheap filter and the lens. You can add fingerprints to deepen the effect. Black pantyhose stretched over the lens also works pretty well. It's possible that you may see patterns in that as well, but pantyhose is generally woven tigher than Softnet filters.

Hoya has a line of soft focus filters that are pretty good. A step or two above Tiffin's, in my opinion.