Little is known about the trade-off between response rates and sample selection on the one hand and costs of different incentives on the other hand in mature online panel surveys. In wave 5 of the Panel Survey of the Swiss Election Study (Selects), a conditional CHF 20 (cash) is used for the politically least interested, while the remaining sample is randomized in two incentive groups: a conditional CHF 10 (cash) and a lottery (5x300 CHF). In the two experimental groups, there are only small differences regarding sample composition, and response rates are only slightly higher in the more expensive cash group. Given that costs are significantly lower in the lottery group, we conclude that it may be possible to save costs on incentives in a mature panel.