I went to Sharath's retreat in 2004 and stayed at the retreat center, but a few of my friends were coming to meet me and it was up to me to find them accommodations elsewhere. Once I realized how many amazing places there were to stay right on the beach, I really regretted staying at the center. Even if it was by default, you lucked out! I can't remember the name of the place I found for them, but there are a few amazing beach shack type places right on the water right by Asvem beach. It's about a 5 minute scooter ride from the retreat center. You'll want a scooter in Goa regardless.

When you arrive, I suggest you go to the retreat center, have them hold you things for the afternoon and scout for a place on the beach. Alternatively, get a hotel somewhere for that first night, get a scooter the next morning and check things out. If my memory serves me correctly, I think they were charging approximately 500INR where my friends stayed. It was a very low-key kind of place: literally a straw beach shack with a shared bathhouse, but that's really all you need in Goa.

Have a great time!