It comes out to $50 for 2 months of Unlimited plan, plus the cost of a SIM card. Not bad for someone looking for a temporary service to port to for 2 months. Since there are no contracts, you can port out at the end of 2 months or continue if it fits your use.
Not verified, but FAQ is vague about this offer being valid on any plan, so technically you can subscribe to the $35 plan (Unlimited Talk/Text, 3Gigs of 4G) and end up paying $17.50/month for 2 months of service. Plus the cost of SIM card.. but better off signing with the $50 plan to avoid any issues.
BTW, I don't know if local stores charge any activation fees.. If so, you can always sign up online.
Check your IMEI compatibility:
BYO Free Month Offer: Avail. for new customers activating on $50 monthly plan, in sel. markets or at boostmobile.com. Not compatible with Family Plan offers or Boost Dealz. Requires initial payment of $50 at time of activation. Credit will be applied to account after activation & payment of 1st month's service. Select iPhone and Android models only. Former Sprint devices not eligible. Customer responsible for any incremental/add'l. charges beyond basic monthly service. Other terms: Boost has no annual svc. contracts; svc. is subject to terms & conditions. Offers/coverage not available everywhere or for all phones/networks. Boost reserves right to change or cancel offer at any time. Prohibited network use rules & other restrictions apply. See participating dealer or boostmobile.com for details.