If you book Norwegian flights using Norway as your home country, round trips to Oslo in March and April are available for under $300usd. $700 for premium economy. It's in Norwegian language and the currency is NOK, but it's pretty intuitive.
For example, if you depart 4/1, and return 4/9, flights are 2,018 NOK or $228.46 USD- round trip. Just select Norway as your country of origin. I think the flights to Guadeloupe and Martinique are similarly priced too. Same dates are $250 using the US version of the site, so it's not that big of a difference; but it's a difference.