Even small monetary incentives, e.g., a one-dollar bill in a postal invitation letter, can increase the response rate in a web survey. However, in the euro currency area, the smallest amount of monetary incentive for a postal invitation is a five-euro bill, which is costly. As such, we conducted a random experiment with prepaid stamp and postcard incentives as affordable alternatives. We compare the effect of our experimental groups with a control group in terms of response rates, response rates in a subsequent wave, data linkage consent, and data collection costs. Compared with the control group, the postcard incentive has no effect on our outcomes except overall costs. Using a prepaid stamp incentive increases the response rate overall but with different effect sizes for subgroups. We find no effect of stamp incentives on response rates in a subsequent wave or data linkage consent.