It's tough to say. It depends on how good your campaign is. I have clients who spend up to $5k but we get them many leads. I can see that being brought down if they wanted less leads.
I'm not saying this because I build adwords campaigns for clients, but the big issue however is that truthfully, it can be a very expensive learning curve for someone who is completely getting started. For someone starting out, it's possible that your first $2k or more is just a learning expense. I wouldn't want a client to say they would do it themselves unless they really wanted to just focus on that.
Seller leads are definitely more expensive and harder to acquire than home buyers and renters are less difficult than those two.
Overall, putting your budget aside, I would ask myself this question if I was in your shoes:
1. How much money is one sale worth to me?
2. How many leads, people, do I need to talk to to get that one sale?
Divide number 1 by number 2 and that is how much each lead is worth.
Example:
1. How much money is one sale worth to me? $5000
2. How many leads, people, do I need to talk to to get that one sale? 20
5000/20 means each lead is worth $250.
And factor in your profit as you want.
In the example above, if you can get 2 leads for $500 from Adwords then you're breaking even if a sale is worth $5000.