Yep, buy once and be happy is what I always say. In your case, and seeing there is a budget that you need to stick to, I would certainly highly consider an HD300. Why? because I don't believe that HD300 (or 500 for that matter) will be your be all end all piece of gear. So why spend more then you have to? It should be considered a transitionally piece for gaining experience and testing the higher end modeling waters so to speak. There is no difference in tone between the 300 and 500 so I wouldn't worry about missing any of that terrific sound you would be hearing from a HD300. While I do always recommend buying the top line stuff whenever possible, I do highly respect the Line 6 HD series. It was this series that got me started on this modeling path in the first place. It was my friends band that opened my eyes to it all. Instead of listening to all the banter on the internet about how bad Line 6 pods sound.. I heard it for myself and discovered a better way to amplify my guitar. Here is the band that changed me seemingly over night. Their entire album was recorded in studio with HD300s while a Black Face Fender sat by with cold tubes.