Do the SIM cards have fixed costs?

If you choose a pay-per-use plan without a subscription fee, the SIM cards do not have fixed costs. 

PERSONAL CUSTOMERS
For Zone 1 countries (including Italy, the rest of Europe, the United States and many other countries), the plan’s pay-per-use rate is €0.12/MB if you use more than 2 MB/month and €0.24/MB if you use less than 2 MB/month. See here for details of the other zones: https://www.thingsmobile.com/business/plans/overview
When data traffic is used by a SIM card, the minimum charge is 1 MB/month. If no data traffic is used by a SIM card, there is no charge.
If a SIM card is not used for more than 12 consecutive months (no data traffic and no incoming and outgoing SMS messages), a charge of €5 will be taken out of the remaining credit.
Traffic is charged in increments of 1 kB, except for in the following countries: Bahrain, Brunei, Cuba, Equatorial Guinea, The Gambia, Israel (Hot Mobile), Laos, Malawi (Telekom), Malaysia (Celcom), Moldova, Oman, Pakistan (Warid), Russia (VimpelCom), Sri Lanka (Mobitel), Sierra Leone, Vietnam (10 kB); Iran (20 kB); Qatar (Ooredoo) (30 kB); Pakistan (Pakistan Mobile) (100 kB); Tajikistan, Uzbekistan (1024 kB).
Each SMS message sent in zone 1 countries costs €0.18 (with the exception of Argentina and Brazil, where each message costs €0.35, and the United Arab Emirates and India, where each message costs €0.60). In zone 2 countries, the cost per message is €0.35. In countries in all other zones, the cost per message is €0.60. The cost of sending SMS messages from another operator to Things Mobile SIM cards (the country code of which is +88) depends on the operator’s rates. SMS messages can be received when there is credit in the account or data traffic on the SIM card.
Things Mobile SIM cards cannot handle incoming and outgoing voice calls.
The rates include VAT where due.
You can find more information at thingsmobile.com
BUSINESS CUSTOMERS
For Zone 1 countries (including Italy, the rest of Europe, the United States and many other countries), the plan’s pay-per-use rate is €0.10/MB if you use more than 2 MB/month and €0.20/MB if you use less than 2 MB/month. See here for details of the other zones: https://www.thingsmobile.com/business/plans/free-sim-card
When data traffic is used by a SIM card, the minimum charge is 1 MB/month. If no data traffic is used by a SIM card, there is no charge.
If a SIM card is not used for more than 12 consecutive months (no data traffic and no incoming and outgoing SMS messages), a charge of €1 will be taken out of the remaining credit.
Traffic is charged in increments of 1 kB, except for in the following countries: Bahrain, Brunei, Cuba, Equatorial Guinea, The Gambia, Israel (Hot Mobile), Laos, Malawi (Telekom), Malaysia (Celcom), Moldova, Oman, Pakistan (Warid), Russia (VimpelCom), Sri Lanka (Mobitel), Sierra Leone, Vietnam (10 kB); Iran (20 kB); Qatar (Ooredoo) (30 kB); Pakistan (Pakistan Mobile) (100 kB); Tajikistan, Uzbekistan (1024 kB).
Each SMS message sent in zone 1 countries costs €0.15 (with the exception of Argentina and Brazil, where each message costs €0.30, and the United Arab Emirates and India, where each message costs €0.50). In zone 2 countries, the cost per message is €0.30. In countries in all other zones, the cost per message is €0.50. The cost of sending SMS messages from another operator to Things Mobile SIM cards (the country code of which is +88) depends on the operator’s rates. SMS messages can be received when there is credit in the account or data traffic on the SIM card.
Things Mobile SIM cards cannot handle incoming and outgoing voice calls.
The rates do not include VAT where due.
You can find more information at thingsmobile.com