You have a number of options but you haven't told use everything wee need to know... I find there may be little need to daisy chain any routers. You should be able to get away with a single wireless router. Sharing the various files, once everything is connected on the same network, can be done for none or all of the computers running.. It's possible to make free hi-gain antennas for all computers and routers needed but you'll want to get the wireless router out of the basement, if that's where it is currently.. Hi-Gain Directional antennas may be the way to go for the machines in the all the different locations trying to connect directly but much is dependent on what you already have.
Free Wireless Antennas
I've used the example below and placed it on wireless routers for myself and a few customers.. It's amazing how such a small device can kick up the gain:
EZ Parabolic Antenna with Template and Instructions
If you want to get serious, use an old satellite dish or an old metal colander to create a great antenna and put it outside the garage, pointing at the house. Depending on distance and how much cabling you already have, you might have an option to run ethernet cable from the cable modem in the basement to the bedroom computer where you could then connect the router with a sufficient hi-gain antenna to cover both the basement computer and the garage computers.
Unfortunately, your request to not buy "anything" leaves us wanting to know EXACTLY what you already have.. WHERE are the routers currently? In the basement? How much ethernet cable do you already have? Which computers already have wireless cards?
If you're stuck on leaving the garage computers "wired", then a simple switch for around $10 and two more short ethernet cables to split the connection would allow you to connect wired in the garage.. That's assuming you already have a long ethernet cable running between the garage and the house.
Hope this helps and let us know more.
I have a Linksys WRT54G and a Linksys WRT54GS wireless routers. I have a cable modem in the basement along with a computer I want to use as on the network file storage and sharing. I have one computer on in one bedroom which is used by one member of my family that sometime needs access to files on the "common" basement PC. I have two computers in a remodled garage with only one ethernet wire available; but insufficient wireless signal strength to use wireless. My sons who occasionally visit have laptops which can access my wireless network in only limited rooms. I want to "daisy chain" (wired) the 2 routers so that I have More wired access in the converted garage and secondly extend the range on my wireless. I want to do this without buying more hardware or having to add additional wiring. Can this be done? and how.