i own a country targeted property site, today someone approach me to buy over my site but i'm not sure how much should i offer (actually i don't plan to sell, but still interested to know at what prices they can accept )

My web detail :
Spend : Not sure, i think up today around 5k (exclude working hour).
Niche : Property Classifieds Search.

Traffic: Now 260k UV monthly (increase 10-25% monthly, base on pass record)
pageview : 1.2m Monthly
Income : 12000 - 18000.
Expenses : 1000 (hosting and some script buying, exclude my personal time)
Time Spend : weekly 5 hour on site. 20 hour look for client/sponsor.
Company size : me and two part timer coder and designer.

Reason don't want to sell : A lot potential and still not reach the limit yet, my second/sub plan/product implement soon.

Reason to sell : some amount that can't refuse or can help me to boost my second site.

Any opinion guy ? How much should i offer or just ignore them ?