Hey guys! Wow it's been a long time since I've been on these forums

Ok so as an update to my travelling: I've now been away from the UK for close to 8 & 1/2 months. Spent 3 months in SE Asia and then migrated to the land down under where the plan was to work and travel (although I have spent the entire time in Melbourne and not really done any travelling).
I've finally decided it's time to come back home again. However, on the way back I'm thinking of stopping off in Vietnam for a little reminder of Asia before getting stuck into the old routine for good when I'm back in the UK. Now I will have a budget of around US $750, which I'm aware isn't massive (only just decided on returning home a few days ago!), but I'm more than happy to stay in hostels, share houses, eat street food and just generally travel on the cheap.
Now I know this is one of the most frequently asked questions, but: realistically how long could one expect to travel around Vietnam for with that kind of money? I have a rough idea based on my travels around Thailand and Laos but was wondering if anyone who's been to Vietnam could give me a clearer idea.
More than happy to answer any questions you may have (yes I do realise this post is quite vague with details)
Thanks, happy travels