Yardenit actually has two souvenir stores, at the main entrance and exit going to the Yardenit Jordan River Baptism Site and a small stall cum eatey located in the baptism grounds, just beside the rest rooms. These souvenir stores have all the obligatory souvenir items, both the secular like fridge magnets, post cards, key chains, books, t-shirts, wood carvings, etc. and the religous items like Olive Wood Crucifixes, rosaries, scapulars, bottle jordan river holy water, religious statues and more.
From their website:
GENERAL HOURS OF OPERATION
The site is open 364 days every rear ; Yardenit is closed on the religious holiday of Yom Kippur (The day of Atonement)
March through November:
Sunday - Thursday and Saturday 8:00am - 6:00 pm (Baptismal ceremonies until 5:00 pm)
Fridays 8:00am - 4:00 pm (Baptismal ceremonies until 3:00 pm)
December through February:
Sunday - Thursday and Saturday 8:00 am until 5:00 pm (Baptismal ceremonies until 4:00 pm)
Fridays 8:00 am until 4:00 pm (Baptismal ceremonies until 3:00 pm)
On the Eve. of certain holidays:
such as Pesach (Passover) Rosh Hashanah (The Jewish New Year), Yom Kippur ( Day of Atonement) and Yom Haatzmaut (Independence Day) the hours are 8:00 am through 1:00 pm. (Baptismal ceremonies until noon)
What to buy: all the souvenir items (both religous and secular) you can think of and it includes souvenir items from nearby pilgrimage areas like tabgha, mount of beatitudes and capernaum. how about holy water from the jordan river.
What to pay: pirces here are fixed
The Souvenir shop within the Visitors Center is designed in the form of a bazaar in a Galilean style typical of the time of Jesus. It sells numerous holy items and rents robes and towels to the visitors, who take home a Baptism or a Rededication certificate.
You can see my Certificate which proves that I visited Yardenit and made an ablution there (unfortunately I haven't been baptized since childhood…).