The Space Centre may be a bit ambitious, that is a formal conference venue and that can be pricey.
Actually we are very resonable and I happen to know one of the Managers there
If you are looking for a venue close to transport links, with a bar and stage then you need to speak to either http://www.themusicianpub.co.uk/
Both have room, stage and bar to hold a nice event in the evening.
Alternatively there is Jongleurs that have the upstairs room that is usually used for comedy, but can be hired in the week. It is within walking distance of the train and bus station.
There is also the Little Theatre, close to Jongleurs, which is run as an amateur theatre venue, but hire is also available. It would cost a little more, but maybe selling tickets for an evening stage show would help cover the costs and ensure the traders are not charged too much (maybe ask The Cogkneys, Broadarrow Jack and the Count to pull together something a little more commercial to support this.
Other venues close to the train station include The Grand Hotel, but it has become a Stag and Hen party hotel recently, so be prepared for chavs.
Obvioulsy the National Space Centre is another option and there are many ways you can do this, depending upon dates.