Something currently cheap in a store do not mean there is no cheaper alternative.
For the last 2 days I mined 24/24 on the DOLP pool with my 2 littles rigs (2.376 mh/s).
I received an average of 195306.5 DOLP per day.
So for the last 2 days we mine 82200 DOLP/mh/day.
The lowest price on Betarigs is currently 0.0004 BTC/mh/day.
So...
with 0.0004 BTC you can mine 82200 DOLP
or
you can buy 40000 DOLP at 1 satoshi each (or worse, get only 20000 DOLP if you want an insta-buy at 2 satoshi).
It's better to mine DOLP. However do not mine to dump and hope to make profit in BTC. There is not enough buyers. You may not be able to sell everything you mined. (Of course, this is only my opinion. Maybe I'm wrong and the price will go up in a near future. You are free to invest or not
)