many options exist for low cost, homemade antennas. yes cheap thin wire as others suggest. an effective small antenna takes some effort so be patient, especially in this time of solar flux. a company makes an antenna called buddi-pole: homemade versions of this antenna are encouraged check the web for plans.
note a ubitx can be taken to a park - so perhaps acquire a medium sized gel cell battery and a portable antenna. do find other hams who live nearby with similar passion for portable/low power operating. an end-fed half wave antenna can be homemade - it just requires a toroid and a fixed capacitor (recipes on the web). here in US a little enterprise called QRPGuys has portable antenna stuff.
enjoy the ride and be patient learning - welcome to world-wide ubitx community.