It really depends on what type of satellite you're talking about.
There used to be satellite SNGs 9 handed where top two win the prize to a much bigger tourn and third place takes down a break even cash prize so that's reasonable. If its one of those tourn satellites where you have to beat like 1000+ people for 20 seats then that's an entirely different beast.
The quick and easy answer is to look yourself up (if you don't know your record) in that type of tourn (i.e buy-in, structure, game etc) to see how well you do then decide if its worth your time and investment. Like if you normally don't see a final table on a regular basis with that type of tourn you're interested in playing but you need to reach the final table for the prize then that saty might not be for you.
If you're online I would look for
freerolls and those type of SNGs I mentioned. Nobody ever goes broke playing freerolls and cashing in SNGs depending on the structure and who you're playing against generally would be easier than going though a massive amount of people.
The other thing with an SNG is you could strengthen your
odds by looking folks up online to see if they're winning players. You don't have to pay for a few searches on
sharkscope or Pokerprolabs, so its free. If you play live then you might have played against the folks you're against at a previous SNG or at the cash table, so you still might have a clue want you're up against.
If its a freeroll and you have the time then go for it regardless. The only thing that will happen at worst is your profit graph will flat line. But regardless of what you decide I would suggest looking up previous results or if playing live (if possible) to just go down to the casino during one of these satties you're interested in to get a clue what you're getting yourself into (i.e having to play for 5-6 or more hours for example when you don't want to commit to that).