If you can find a radio amateur club in your area, they could be a good resource.  They have a competitive event called fox hunting, which involves locating a hidden transmitter.

Anyway, a directional antenna for 401MHz can be made easily and cheaply but you have to know what you're doing.  The cheapest (USD20?) radio receiver is an SDR dongle for your laptop or Android phone, but again you have to know what you're doing.

Using this setup would be like tracking a VHF animal tag, you swing the antenna around until you get the strongest signal and go that way.  It would not be like using the Argos CLS, you don't get a GPS location of the tag, and it doesn't identify any tags it picks up.

1/ A goniometer is a type of receiver which can measure an angle and then tell you where your signal is coming from in a specific frequency band. It is much more complicated to develop which explain price.

2/ With a basic receiver using a YAGI antenna, you will have to get the signal location by turning around. If the receiver is not enough sensitive and if the antenna is a bad quality, you won't get signal at all. You can lose lots of time.

3/ With a basic receiver using an omni-directional antenna, you will get the signal but you won't know where the signal is coming from. Same as before, if the receiver is not enough sensitive and if the antenna is a bad quality, you won't get signal at all. Depend what you are looking for.

I hope this will help you to better understand differences between these tech. 

If you need more informations, you can contact me directly by mail at virginie.perilhon@xerius.fr

The CLS Goniometer is an excellent tool for the job - I believe it is also available to rent (at least it used to). 

If you want to go the low-budget route I would consider building a cross antenna with 4 yagi's, connect these to some kind of 4-channel receiver, and use the relative differences in intensity between the orthogonal directions to estimate the angle of arrival. You would need a way to simultaneously change the Rx gain on the four channels. Remember the transmission rate much lower than a typical VHF transmitter so it will take a while to find a tag this way. Using a single yagi would be basically impossible unless the sea is a mirror and the tag not moving in the waves.