Until I plan my exact trip route, book places to stay, and figure out what (if any) tech conferences I'm going to, it will be hard to determine an exact budget for my trip. However, I can create a ballpark figure based on averaging an aggressive budget and a conservative budget. "Conservative" in this case means I try to spend as little money as possible while in the aggressive estimation I do not worry about most of what I'm paying throughout my trip.
General expenses to estimate include (in rough order of magnitude):
Again, this is the most conservative estimate if I plan to spend as little money as possible.
Let's average about $75 a night for rooms. Some cities will obviously be much more expensive than others. I'll also have to stay outside the main areas of most cities to get a decent rate or watch for particularly good deals on Airbnb. Couch surfing is also an option.
120 nights * 75 = $9000
$9000 actually isn't too bad considering I would pay about $7000 for my rent & utilities from mid-March through the end of July anyway.
Assuming I go about 9000 miles, I get 20 MPG (I get worse gas mileage with the top down), and gas hovers around $5 a gallon (I need premium fuel for the S2000), I'll spend about $2250. Add another $250 for oil changes and other random things adds up to $2500.
This one seems the most difficult to estimate because it really depends on how much I eat out while traveling. Obviously I won't have access to a kitchen most of the time. But I usually eat a lot of raw fruit and nuts anyway, so I don't see this as much of an issue.
I will still have to eat out when I want a regular meal, but for the most part I'll shop at grocery stores I find along the way. Let's say I eat out half the time (~60 nights), spend $40 on average throughout breakfast, lunch, and dinner (sometimes way higher, other times way lower), that comes out to 60*40 = $2400. Round up to $2500 just to make it even with gas & car maintenance.
Yikes, this is the most difficult one to estimate. My cell phone plan with a data connection (including wifi hotspot) costs $120 a month. parking depends on where I stay and what places I visit. Tolls depend on what roads I take. I'll punt and say $500 a month, so about $2000 additional throughout my trip.
Conservative total: $9000 + 2500 + 2500 + 2000 = $16000.
This seems low to me but perhaps I'm just really used to Washington, DC prices.
This is a reasonably aggressive estimate. I'm not looking to stay at the Ritz every night but in some cities it's worth staying in a nice hotel if it has a great location.
Bump from $75 average per night to $125 average per night and we're at 120 * 125 = $15000.
I think this estimate has the least variability in it unless something really bad happens to my car. Let's add $3000 in case I have a bad breakdown plus I spend more money on gas than I estimated in the conservative case. $2500 plus $3000 for aggressive estimate is $5500 total.
I'll double this to $5000 from $2500.
Increase by 150% to $5000.
Aggressive total: $16000 + 5500 + 5000 + 5000 = $31500. This seems high to me but not out of the realm of possibility if I'm not careful about what I spend while on the road.
So those are some spitball figures I threw out. I'm estimating about $16k to $32k cost total for the trip including accomodations, food & drinks, car-related expenses, and other miscellaneous charges. I'll refine the estimates as my plans become more concrete.