Are you buying a for sale by owner where there is no listing agent in addition to your not having an agent?
If so then I suggest you pay for and obtain an appraisal from a licensed appraiser to see what the current fair market value of the home is. I highly doubt an agent will just provide you with a market analysis so you can make an offer on the home, and he/she will not be paid to help make the sale happen.
Either that, or if the seller is willing to pay an agent of your choice, GET AN AGENT, and have him/her do the market analysis, then present to offer to the seller.
A buyer and seller with no agent representation can get tricky at best, and just plain bad at worst.