Looking to buy a couple of bikes that would be good for trail riding in Ohio and riding on the beach in Hilton Head...hard packed beach. Have looked at Trek (Navigator and 7000 series), Diamondback (Wildwood and Serene), and Northrock (SC7 and CL5)...but don't know anything about bikes....would like to spend $500 or less for each bike...obviously the cheaper you go, more trade-offs in quality...so looking for some experienced perspective..