Audio Restoration - Need something good but not too pricey

I've recently converted some old family voice recordings that were made in the 1980s from an old cassette to mp3. The quality wasn't great to begin with, but the quality has deteriorated with the conversion - Lots of background noise, voices distorted, crackling etc.

I'm no pro so I don't want to spend hundreds on professional software. But at the same time I want to clean up the sound quality on these audio files as the content carries lots of sentimental value.

Can anyone recommend a good, relatively inexpensive app that I could use to restore the audio quality, sharpen up the voices and generally clean it up?

Alternatively, could anyone recommend another solution to my problem?

Have looked at tools such as Amadeus, SoundStudio, SoundSoap Pro (Demo plugin) but I don't know where to start. Help would be appreciated!

Thanks!

the only thing i can thing of is soundsoap. it's not that expensive and i think it does what you need it to do.