The less expensive option is to simply make a backup on an external drive of the important stuff including browser settings. Then install linux in your old machine, it will perform much better.

I'd add to replace microzoz programs with open source ones, libreoffice.org and openoffice.org are great alternatives and allow exporting xls and docs in case your clients need it. Alternatively, cryptpad.org offers great online alternative as collaborative online workspace, everything encrypted, for real.