Usually $8.74 per issue for print & digital or $6.74 per issue for print only (in a six month subscription). I think to buy it in the newsagent it's around $10 from memory.
For ten weeks only, but since you can set your subscription in the future you could probably buy several and stagger them to get a continuous super cheap subscription. If anyone manages to do that, please share!
I'm not sure when the promotion ends but I know it will - took advantage of a similar offer year before last as a gift.
Digital subscription over 12 months (51 issues) available for about $2.76 per copy on zinio. I know it's more expensive than the deal but it's over a longer period.
https://www.zinio.com/new-scientist-m3215
Above deal results in a recurring 3 monthly subscription for $120 every three months unless you cancel.