This is something of a difficult problem that you face in consulting - you need to give a rough cost to get a contract signed before allocating resources. There just isn't a great answer to a lot of these problems, but here's a few tips:
1) You might want to first attack the problem by 'breaking it down' into smaller tasks that you can have a chance at estimating. Something like "I need to create a billing system, which will require that I have a database, a login feature, a list of current invoices, a way to edit a single invoice, a way to approve an invoice for payment, etc., etc.)
The smaller pieces you can define, the better chance you'll have at producing a reliable estimate.
2) See if you can't shoehorn a dev or two (buy her lunch!) into giving some advice - even at a high level you can define a "large" task, a "small" task, etc. Try to break the "large" tasks down even further if you can.
3) Now if you have a rough number in mind (think large chunks here - "this might be XXX days of work"), then you can think about resource assignment.
But to echo an earlier comment - I've never seen an 'analyst' ultimately responsible for estimation and resource assignment; to come up with a reliable estimate you do need someone with enough experience (and preferably a track record of actually tracking "estimates vs. results") to know what amount of effort certain tasks might take. (Again, preferably the opinions of "more than one" of these people.)
The problem is similar to me planning a house building project: I can draft a bunch of back of the envelope projections, but at some point I'm going to have to get the opinion of a carpenter who actually builds houses.