It's quite possible to start out as a travel agent from home with a desk, a PC and a telephone line. You can start to build up a client base from among friends and family so it isn't technically difficult to get started.
But you do need to think bigger than this if you want the business to survive. Competing on a local level or around the high street are both non-starters to a successful business. A truly local business won't survive in such a changing market and the high street will bring you up against the big names. You need to open up to a national audience.
Look into an area that isn't well served already by travel agents. If you can find no obvious reason for this and there is apparently a need for your business, set up there. Alternatively, start a business that isn't office based and that provides something of a niche service.
Martin Jones started Freedom Direct on the back of Teletext rather than on the high street. Never intending to be a walk-in business, his main research was establishing links with the banks because he needed an £80,000 bond to start off. Links with a trade association will again help with things like this.
If you're starting from a secondary location rather than prime retail site, rent will obviously be reduced. As above, specialised travel services are more likely to work with you remotely so it matters less where you're based
However, a remote - if cheaper - location may be a turn off when it comes to recruiting staff. This is not generally an industry where staff is highly paid but there is competition to recruit good people in the first place so additional perks may work well.
Look for people who've worked in the industry before who'll be attracted to the discounted holidays and offer them good working conditions. Roughly speaking, salaries are on a par with office work but as with all jobs you should expect to pay more for extra talents (such as languages) or experience.