If you play the discounts right, you should be able to find an Acurite 5n1 system with their Internet Bridge for $150 or less.
A system with an Internet Bridge sends continuous updates to Acurite's servers (MyBackyardWeather.com) every 18 seconds WITHOUT the need for a dedicated PC running 24/7. You can view your weather data via a web browser or through available smartphone apps.
Acurite can also forward your station data to wunderground at 15-minute intervals out-of-the-box. If you want more frequent updates to wunderground, or wish to report to additional weather networks, then you have to start looking into additional hardware and/or software. There are various approaches for doing this depending on what Acurite hardware you have (Bridge or USB-connected console) and type of computing hardware you have available or are willing to purchase.
A word of caution when comparing Acurite systems... there are basically three types of 5n1 setups ranging from zero internet ability (the supplied display console has no USB port), to needing a Windows PC 24/7 to report to the internet, to not needing a PC at all by using their stand-alone bridge. If you find what you think might be a big bargain, study the advertised features carefully to be sure you know exactly what you're getting.
Also, be aware the features of the supplied consoles can vary greatly. It's more than just USB connectivity and color. For example, some of internet bridge kits don't have a very fancy console to keep the price down. If the look of the console is important to you, research that carefully.