These large $1 coins from Singapore are made of copper-nickel and are not worth very much. Typically they are worth less than $1 US dollar except when fully uncirculated, when they might reach $5 in catalog value.
The design is intriguing, and they make good conversation pieces. I'd probably spend $2 to $3 to get the one in the picture. It is circulated but with very nice eye appeal.
1978 is a low-mintage date and the price might double or triple for that date. Further, there are some silver proof coins made only for collectors and these contain about one-half ounce silver. Some of the early proof dates, 1975 to 1980, can catalog around $50.