oh, deja vu ... i had to furnish 8 guest rooms, dining room, common areas, porch, kitchen ware, dishes, appliances, etc. and it was so hard. since you ask, i assume you don't have deep pockets. i would have loved to shop and buy room suites but could not.
spend THE MOST money on the mattresses and box springs (biggest you can accommodate). then mattress covers and pillows, bed linens and towels/shower curtains. your guests must be comfortable sleeping. all you need are bed frames and you can make headboards or find them all over the place. you need room darkening curtains.
all the rest of your furniture can be pulled together from consignment, second hand, discount, yard sales, estate sales whatever ... but avoid particle board like the plague. and i prefer to buy upholstered items from stores for obvious reasons.
as income increased, i filled out each room. but there is so much you need. from end tables and lamps to clock radios, mirrors, bureaus and luggage racks!
i saved pictures of my favorite rooms at b&b's and from magazines as inspiration. especially the rooms at places of members here -- i'd look at them and think ... can i approach anything like that?
good luck.