Apart from having a party at your home, please note that there are also many other affordable alternatives. For example, the cities of Helsinki and Espoo have dozens of kindergartens and similar venues to hire (and most of them even include plenty of toys to play with during the party).

Please see below links to lists of such venues of both cities – and remember: these places will look totally different with CaroDeco decorations!

Helsinki: http://www.hel.fi/www/Helsinki/fi/paivahoito-ja-koulutus/leikki-ja-avoin-toiminta/leikkipuistot/vuokraaminen/
Espoo: http://www.espoo.fi/fi-FI/Paivahoito_ja_koulutus/Paivahoito/Yhteystiedot/Vuokrattavat_tilat

Note that some of these venues are very popular – so remember to book early.