A lot of Sunfish sailors buy the Harbor Freight boat trailer for a 15' boat at under $400. It comes disassembled but has lights, safety chain etc, and is roadworthy at highway speeds.
Buy them on-line with the usual 20% off coupon that HF offers most weeks. I know two Sunfish sailors who bought them and were happy with them. HF stuff is usually pretty
shoddy but in this case they must meet minimum US DOT standards, so they are a bargain.