Nonnative, invasive grasses displace native plant communities and challenge ecological restoration globally. Ecological monitoring of restoration is typically short term and rarely reassessed to determine if initial findings are indicative of multiyear outcomes, and economic costs of restoration are seldom quantified. To address these knowledge gaps, we resampled a restoration experiment in an invasive Megathyrsus maximus—dominated ecosystem in Hawai'i to compare success of restoration treatments at 8 and 36 months. We calculated cost to establish and maintain (for 3 yr) experimental field trials (0.13 ha) and management-scale (1 ha and 10 ha) units, estimated 30-yr costs for management-scale units, and determined key drivers of costs. Survival of native outplant species did not differ between 8- (56%) and 36-month (51%) monitoring periods, and M. maximus cover was lower in restoration treatments than in control plots at both time periods. Cost to establish and maintain the experimental trial was $14,299 (Present Value at 2% annual discount rate, 2015 US$; $109,993 ha^-1). Scaling up restoration to 1 and 10 ha units produced economies of scale, with 3 yr costs declining with increasing area ($149,918 ha^-1 for 1 ha; $124,139 ha^-1 for 10 ha). Total Present Value to restore and maintain a 1 ha site for 30 yr ranged from $153,195 to $302,917 ha^-1, varying primarily based on labor and seedling costs. This study demonstrates that early restoration results can be indicative of longer-term results, establishment expenses drive long-term costs, and restoration efforts are most cost-effective when maintained over large spatial scales and long time periods. Importantly, this study allows other projects in the region to estimate restoration costs based on site-specific criteria.