Oh I used to feel like this too. We have no family nearby and all of the social groups closed down for the holidays leaving me feeling totally stranded.
My survival mechanism was to break each day up into chunks, of about 45 minutes each. I didn't stick to the timetable if we were having fun and could let something run on, but used to have a list on the fridge door, so that I could check what we were supposed to do next, if the day ahead suddenly seemed very long. It kind of drove us forward through the day. In order to survive, two trips out of the house were essential for me. We fed a lot of ducks, went to wave to trains nearby our house, went on the swings, went to the library or jumped in puddles. Twice every day. If we had a dvd or a programme we enjoyed we also spent longer watching TV.
6.00 - 6.45 - Telly time
6.45 - 7.30 - bath (yup - we had a lot of baths. Great value for money with a few empty yoghurt pots to play with.)
7.30 - 8.15 - breakfast
8.15 - 9.00 - lego time
9.00 - 9.45 - walk to the playground/welly walk, jumping in puddles
9.45 - 10.30 - snacktime. Make toast shapes to eat with jam
10.30 - 11.15 - playdough
11.15 - 12.00 - sweeping up with dustpan and brush
12.00 - 12.45 - build a den under the table
12.45 - 13.30 - lunchtime (may be able to eat in the den)
13.30 - 14.15 - walk to library
14.15 - 15.00 - read in library
15.00 - 16.30 - walk back from library, with snack on the way
16.30 - 17.15 - telly time
17.15 - 18.00 - supper
18.00 - 18.45 - bathtime
Have you got a library locally? We used to use them a lot for cheap rented dvds. Other cheap activities include: papier mache model making (cover a balloon in papier mache to make 2 masks); mask painting; balloon tennis in the lounge (bashing a balloon to and fro); cooking; painting/drawing pictures; hotwheels cars; story time/books; dressing up; makeovers; singing/lounge disco; swimming or soft play (had a cheap one locally); popcorn making; pasta necklaces/popcorn necklace making; playing shops; baths at any time of the day; indoor sandpit (I used our old babybath and filled it with playsand/yoghurt pots); hide and seek; tickle fights . . .
Hope that helps. I would switch activities every day for the list, but if they wanted to build another den or whatever, that's OK - you can switch back. Don't feel guilty about you being bored (I hated being at home with toddlers) - just get through each day with a variety of short activities for them to do.
Best of luck. If the weather's nice, it will be so much easier than Feb half term.