The only caveat I would add to estatereal's good advice would be that if your strengths lie in other areas than the one you're hiring for, perhaps hiring someone with the appropriate experience and skills will save you money in the long run.
That being said however, a good rule of thumb is if you can do the job yourself (have the time and skill), do it yourself.
You said:
[quote=RaquelMangual]I feel like I need an assistant, but can't afford one on a regular basis.[/quote]
The truth is, if you really are at a point where you [b][i]need[/i][/b] an assistant, you'll be able to afford one.