My advice: forget even spending $5 on a hydrometer and get a refractometer. You can find them for $45-60. They are more expensive, but the hydrometer may cost you more in livestock in the long run. I had a hydrometer and it read 1.025 in both of my tanks. I decided to buy a refractometer, and my one tank was at 1.031, and the other at 1.024. That's a big difference. I would DEFINITELY spend the extra little bit of $$ it costs to get a refractometer and do it. Like I said earlier, it could possibly save you more money in the long run rather than risk dying/dead livestock while thinking your salinity isn't the problem.
EDIT: And to answer your question, $35 for a hydrometer is quite high. I got mine for $19 from my LFS and I thought that was pretty steep.