You can find used Garmin 220’s for around $200 on eBay and dog hunting sites sometimes. They are outdated and hard to get repaired, but they would work fine for what your doing. Depending on what kind of dog you use and how you train it....you might not even need a tracking collar. Some guys use a 15-30 foot lead and some guys let the dog work free style and put a bell on their collar. Check with Outdoor dog supply, they sale used and/or refurbished units. I’ve dealt with them before and was thoroughly satisfied with the service I received.
X2 on Outdoor Dog Supply or Gun Dog Supply. A lot depends on your budget as these things can get pricey. The Garmins are the way to go and you need to decide if you want to just track or be able to track and “train”. The alpha 100’s have dropped a bit since the 200 has come out. I just got the 200 and it is pretty much unbelievable. Go to YouTube and watch a few videos about the Astro and Alpha.